Introduction to Life Science, Earth and Life Science PDF

**Introduction to Life Science, Earth and Life Science** The Evolving Concept of Life Life is believed to have existed on earth for billions of years now. Scientists do not know exactly when did life begin on Earth. However, they are able to trace how life developed and evolved using some pieces o...

**Introduction to Life Science, Earth and Life Science** The Evolving Concept of Life Life is believed to have existed on earth for billions of years now. Scientists do not know exactly when did life begin on Earth. However, they are able to trace how life developed and evolved using some pieces of evidence. **The Origin of Life** There are many theories about the origin of life. Some believed that living organisms were put to Earth by some divine forces. Others say that life did not originate from Earth but from other planets. But among scientists, the most accepted theory is that life came from inanimate matter. According to the **primordial soup theory** proposed by **Alexander Oparin** and **John Haldane**, life started in a *primordial soup of organic molecules*. Some form of energy from lightning combined with the chemicals in the atmosphere to make the building blocks of protein known as the amino acids. **Early Forms of Life** ======================= The first form of life is believed to have appeared some 3.5 billion years ago. The first evidence of life is found in microfossils. **Microfossils** are fossils that contain the remains of tiny plants and animals. They are very small and can be measured in millimeters, and some could only be identified under a microscope. Some of the remains of organisms do not have a nucleus so they were called **prokaryotes**. They are known to be the earliest forms of life. They have survived the extreme conditions of the early environment. They started to make their own food by utilizing the energy from the sun and the carbon dioxide in the atmosphere. These are the **photosynthetic organisms**. The process of photosynthesis produced more oxygen that changed the Earth's early atmosphere. This change in the atmosphere allowed oxygen-breathing organisms to exist. The **cyanobacteria** are the first photosynthetic organisms to form. Their microfossils are among the easiest to recognize. Their morphology remained the same and they left chemical fossils in the form of broken products from pigments. The first microfossil that showed remains of organisms with differences in structure from the simple form of life was seen in rocks about 1.5 billion years old. They are larger than bacteria and have internal membranes and thicker wall. These findings marked the beginning of eukaryotic organisms on Earth. **How did multicellular organisms evolve?** ------------------------------------------- Multicellular organisms are believed to have evolved from unicellular eukaryotes. Some single eukaryotic cells, like unicellular algae, formed multicellular aggregates through association with another cell producing colonies. From colonial aggregates, the organisms evolved to form multicellular organisms through cell specialization. **Protozoans**, **sponges**, and **fungi** came to being. The first fossilized animals which were discovered **580 million years** ago were *soft-bodied*. The continuous process of cell specialization brought the emergence of complex and diverse plants and animals, including human beings. Evidence from fossil layers proved that different forms of life were present and have evolved through time. According to Charles Darwin, organisms change over time as a result of adaptation to their environment in order to survive. **Key Points** - The first forms of life are the bacteria found on microfossils. - Eukaryotic cells evolved from prokaryotic cells. - Multicellular organisms evolved from eukaryotic cells through cell specialization. - The evolution of life is brought about by the changes in the environment which are linked to changes in climate and geology. - Evidence that life evolved is found in fossil records and molecular biology. **Classical Experiments that Lead to the Discovery of First Life** **How did life begin on Earth?** About 4.6 billion years ago, the Earth began to exist. The existence of life, as believed by many scientists, started from the moment the Earth's environment became stable to support life. Several theories were proposed to explain life's origin. One of these theories is the **primordial soup theory** proposed by **Alexander Oparin** and **John Haldane**. According to this theory, life started in a *primordial soup of organic molecules*. Chemicals from the atmosphere and some form of energy from lightning combined to make amino acids which are the building blocks of protein. Several scientists conducted different experiments that modeled conditions which may have enabled the first life forms to evolve. Among these experiments are the Electrical Discharge Experiment, Thermal Synthesis, and The Protocell Experiment. **Electrical Discharge Experiment** =================================== **Stanley Miller** and **Harold Urey** verified the primordial soup theory by *simulating the formation of organic molecules on the early Earth*. They confined methane, ammonia, water, and hydrogen in a closed system and applied continuous electrical sparks to trigger the formation of the building blocks of life. After a day, they observed a change of color in the solution. After a week, the solution was tested, and they found out that several amino acids were produced.  C:\\Users\\ACER\\Desktop\\SHS11-12\\1.Earth and Life Science\\2nd Quarter Earth & Life\\SCI (Phy Sci) Miller-Urey Experiment.png\ \ The purpose of this experiment was not to try and produce amino acids, rather, its purpose was to explore the conditions of the early Earth and what the naturally occurring results would be. **Thermal Synthesis** ===================== **Sidney Fox** demonstrated in his experiment the origin of life using a specific mixture of pure, dry amino acids. In his experiment, after heating the mixture, an aqueous solution was formed and cooled into microscopic globules called **protenoid microspheres**. The globules looked like coccoid bacteria and seemed to be budding, which is a form of reproduction in some microorganisms.\ He claimed that the protenoid microspheres constituted **protocells** -- almost true cells, and multiplied through division like true cells. He believed that these cells were the link between the primordial environment and the true living cells. **The Protocell Experiment** ============================ **Jack Szostak** contemplated on how early life forms formed in a primordial chemical environment. He then thought that the simplest possible living cells or protocells just required two components to be formed: a **nucleic acid genome** to transmit the genetic information and a **lipid sac** which encapsulated the genome and let itself grow and divide. Szostak built lipid sacs made in fatty acids and a **replicase** -- an RNA molecule that catalyzes its own replication, in the test tube. He found out that lipid sacs with more RNA grew faster. He suggested that such test tube evolution was possible. The results suggested that the early forms of life with just a single gene, an RNA gene, could have undergone a Darwinian evolution. **Key Points** - One of the theories about the early forms of life is the **primordial soup theory** proposed by **Alexander Oparin** and **John Haldane**. - Several scientists conducted different experiments that modeled conditions which may have enabled the first life forms to evolve; these include **Electrical Discharge Experiment**, **Thermal Synthesis**, and **The Protocell Experiment**. - **Stanley Miller** and **Harold Urey** verified the primordial soup theory by *simulating the formation of organic molecules on the early Earth*. - **Sidney Fox** demonstrated in his experiment the origin of life using a specific mixture of pure, dry amino acids. - **Jack Szostak** made protocells from a lipid sac and a replicase -- an RNA molecule that catalyzes its own replication. **The Connections and Interactions Among Living Things\ How are these units connected to each other?** **Ecology** =========== **Ecology** is the branch of biology that deals with the study of living organisms and their relationships with each other and their environment. Let's take the diagram in the previous slide as an example. The diagram depicts that everything is connected and interrelated with one another. They are different from each other, but they co-exist with one another in one community. The unifying themes of life give us an idea of how each of these themes contributes to the connection and interaction of living organisms and their environment. **Biological Systems** ----------------------  A system consists of related parts that interact with each other to form a whole. It has different parts, but each plays a significant role for the whole to function as one. Without the help from each other, it cannot fully perform its function. **Levels of Organization** -------------------------- The cells are considered as the basic unit of life. All living organisms are made up of cells. When cells come together, they form the tissues. A group of tissues that perform the same functions form the organs. A group of organs that works together form the different organ systems. An organism consists of many organ systems but functions as one individual. **Forms and Functions** ----------------------- The function of an organism or a part of an organism greatly depends on its form and structure. It is related to how it works. An example of this is the webbed foot of a duck which helps the duck swim and search for their food under water. Others birds have different structures of feet used for perching and grasping food. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Reproduction and Inheritance** -------------------------------- Reproduction ensures the survival of species. All living organisms reproduce either through asexual or sexual reproduction. In asexual reproduction, the offspring inherits the genes from a single parent. However in sexual reproduction, the offspring inherit the genes from two individual parents. Some examples of animals that undergo asexual reproduction include earthworms, hydra, planaria, and bacteria. Animals that undergo sexual reproduction include some reptiles, fishes, insects, and mammals. **Energy and Life** ------------------- Living organisms obtain energy from the food they eat. Plants undergo photosynthesis where they convert the energy from the sun into sugar. Since most of the animals cannot produce their own energy, they get the energy from the consumption and assimilation of the biomass of plants and other animals. **Thermal Regulation** ---------------------- The ability of an organism to regulate their internal conditions is called **homeostasis**.\ Humans have to maintain a body temperature of 37 ∘C. When the temperature outside our bodies becomes hot, the skin cools down by perspiration, maintaining the normal body temperature. **Adaptation and Evolution** ---------------------------- In a world that is continuously changing, life itself evolves. **Evolution** is the change in the physical and heritable traits of organisms over successive generations. Organisms change over time to acclimate to their environment in order to survive. If they fail to adapt to the changes, they usually become extinct. The Baiji white dolphin, for example, became extinct due to diminished food supply and in addition to that, the pollution caused by human activities. One contemporary example of adaptation is the *Aedes aegypti* or the mosquito famous for carrying dengue that caused major outbreaks nationwide. Their eggs were able to survive with scarce or no rainwater which is essential to their life cycle. Evolution takes time, usually decades. However, there are times when change happens very rapidly. One example is the blue moon butterfly that managed to undergo a mutation which allows the males to survive an infection of a parasite. **Key Points** - **Ecology** is the study of living organisms and their relationships with each other and their environment. - An organism's structure is related to how it works. - An **organism** consists of many organ systems but functions as one individual. - The function of an organism or a part of it depends on its form and structure. - Reproduction ensures the survival of species. - Living things obtain energy from the food they eat. - The ability of an organism to regulate their internal conditions is called **homeostasis**. - Organisms undergo adaptation or evolution in order to survive. **Bioenergetics** **Cell: The Basic Unit of Life** **Have you ever wondered what the inside of a cell looks like and how its parts perform functions required for life?** **The Basic Unit of Life** ========================== All organisms are made up of cells. The **cell** is the basic structural unit found in every living organism that performs several functions throughout life. The zoo animals such as elephants and snakes, the plants in the garden, and even yourself, are all living things composed of cells. These cells can only be seen through the use of a microscope. **Eukaryotic and Prokaryotic Cells** ------------------------------------ There are two types of cells based on the presence or absence of a nucleus. Cells can be eukaryotic or prokaryotic. **Eukaryotic cells** have a **nucleus** which contains the genetic material or DNA. They also have several membrane-bound organelles such as ribosomes and mitochondria. They include animal and plant cells. **Prokaryotic cells** differ in eukaryotic cells because their DNA is found in a region called the **nucleoid** rather than a nucleus. They also lack most membrane-bound organelles present in eukaryotes. However, prokaryotes have **cytoplasm** where organelles are suspended, **flagella** that aids in motility, **cell wall** made of peptidogycan, **cell membrane** that serves as a selective barrier, and **ribosomes** that make proteins. \  **Eukaryotic Cells** -------------------- There are two types of eukaryotic cells: animal and plant cells. ### **Animal Cells** Aside from the nucleus, the typical animal cell also have other membrane-bound organelles such as mitochondria, lysosomes, Golgi apparatus, endoplasmic reticulum, nucleus, microtubules, plasma membrane, cytoplasm, and ribosomes. - The **mitochondria** is the powerhouse of the cell because this is where most energy (ATP) is produced. - The **lysosomes** break down large molecules into smaller pieces and digest worn out organelles. - The **Golgi apparatus** sorts and packages proteins and lipids produced by the smooth and rough endoplasmic reticulum. - The **cis face** receives the materials for processing in transport vesicles. - The **trans face** is the discharging end where molecules are released through the secretory vesicles. - The **endoplasmic reticulum** has two types: rough ER and smooth ER. - **Rough endoplasmic reticulum** is bounded with ribosomes. It is where most protein synthesis occurs. - **Smooth endoplasmic reticulum** has no ribosomes attached. Its function is mainly for lipid synthesis. - The **nucleus** is the largest organelle that serves as the control center of the cell. It contains the hereditary material known as **DNA**. - The **microtubules** are components of the cytoskeleton and important in a number of cellular processes. - The **plasma membrane** is a semi-permeable membrane that encloses the cell separating its contents from the surroundings. - The **cytoplasm** is a semifluid matrix where organelles are suspended. - The **ribosomes** consist of the large and small subunits. Their main role is to synthesize proteins needed by the cell. ### **Plant Cells** Plant and animal cells share the same structures except for the chloroplast, cell wall, and amyloplast, which are only found in plants. A large vacuole is found in both animal and plant cells but is a typical and distinct structure in a plant cell. https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDUvMjUvMDIvNDUvNDgvY2Q3MTg2MWEtMDFkNC00ZjI2LTkxOTgtMDI0NzhjM2ZhYTRmL1NDSSUyMChMaWZlJTIwU2NpKSUyMFBsYW50JTIwQ2VsbC5wbmciXSxbInAiLCJ0aHVtYiIsIjYwMHhcdTAwM2UiLHt9XV0.png?sha=24c271c6958414cb - The **cell wall** provides support and protection for the cell. Special openings called **plasmodesmata** are used to communicate and transport materials between plant cells. - The **chloroplasts** convert light energy to sugars through photosynthesis. - The **vacuole** is responsible for storing food, water, and metabolic and toxic wastes. - The **amyloplast** is responsible for the production and storage of starch and the conversion of starch back to sugar as needed by the plant for energy. ### **How do cells carry out functions required for life?** Cells have different types which are specialized to perform specific functions. For example, cardiac muscle cells have numerous mitochondrion because they need a lot of energy. Nerve cells are long for them to be able to transmit signals from the brain to the rest of the body. Cell membrane of cells in the intestine is extended to have more surface area to absorb food. Mammalian red blood cells don't have nucleus to make more room for hemoglobin, a protein that carries respiratory gases. **Key Points** - The **cell** is the basic unit of life. - **Prokaryotic cells** do not have nucleus. Their genetic material is found in a region called the nucleoid. - **Eukaryotic cells** have nucleus which contains the genetic material. They can be classified as animal or plant cells. - **Animal cells** have a nucleus and other membrane-bound organelles such as mitochondria, lysosomes, Golgi apparatus, endoplasmic reticulum, microtubules, plasma membrane, cytoplasm, and ribosomes. - **Plant cells** have the same structures as animal cells except for chloroplast, cell wall, and amyloplast which are only found in plants. - Cells have different types which are specialized to perform specific functions. Light-Independent Reaction This is also known as the **Calvin cycle**. It takes place in the stroma and uses **ATP** and **NADPH** from the light-dependent reaction. It reduces CO~2~ to form sugar. The reaction is summarized below. **Key Points** - **Photosynthesis** is the process where plants and other photosynthetic organisms convert light energy into chemical energy to form **sugar**. - Photosynthesis has two phases: **light-dependent reaction** and **Calvin Cycle**. - The light-dependent reaction converts energy to **ATP** and **NADPH**. It has four steps: (**1**) Light absorption and splitting of water, (**2**) production of ATP, (**3**) hydrogen pump powered by the movement of electron acceptors and, (**4**) production of NADPH by re-energizing electrons. - Calvin cycle uses the **ATP** and **NADPH** from the previous reaction. It has three steps: (**1**) Fixation of CO2, (**2**) reduction of 3-phosphoglycerate and, (**3**) regeneration of RuBP from G3P. **The Energy Flow from Environment to Cells** Cells of living organisms need constant supply of energy to carry out life processes. The lions catching their prey, the birds flying through the air, and the dogs wagging their tails -- use energy. **Where do organisms get this energy? How does energy flow from environment to cells of organisms?** **Key Points** - **Autotrophs** can make their own food through a process known as photosynthesis. - **Heterotrophs** consume other organisms for food. They harvest energy through the process known as cellular respiration. - As energy is transferred between living organisms, some energy is lost in the form of heat and body activities. - Only 10% of the energy is obtained when an organism eats the other. - The solar energy is captured in the chloroplast of producers. Through photosynthesis, glucose is produced. Animals could then use this glucose from producers to make their own energy through cellular respiration which occurs in the mitochondria. **How Organisms Obtain and Utilize Energy** Carbohydrates are one of the most important food sources for animals. If carbohydrates are stored, then its potential as a source of energy is null. Carbohydrates must be broken down into sugar and produce ATP that will act as a fuel essential for cell\'s activities and processes. The same thing happens when you put a coin in a machine slot, the machine slot will not accept it unless it is a token because the machine slot was made to read the token, not the coin. **Cellular Respiration** ======================== **Cellular respiration** is a process of energy conversion where carbohydrates are broken down into **glucose** and **ATP**. There are two types of cellular respiration: **aerobic respiration** and **anaerobic respiration**. **Aerobic Respiration** ----------------------- This occurs when glucose is broken down in the *presence of oxygen*. This is divided into three stages: **glycolysis, Kreb\'s cycle**, and **oxidative phosphorylation**. ### ### **A. Glycolysis**  - It is a process where glucose is broken down into **pyruvic acids**. - It takes place in the **cytoplasm**. - Two **ATP** and **NADPH** are produced. - This can happen *with or without oxygen*. ### **B. Kreb\'s Cycle** https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDEvMjYvMTIvMTEvNDkvNTE5MDJmMTgtYjI0OC00ZmE2LWJlNWQtMTQ2Y2NjNzJmZDk5L0tyZWIlMjBDeWNsZV93aXRoTGFiZWwlMjAoMSkucG5nIl0sWyJwIiwidGh1bWIiLCI2MDB4XHUwMDNlIix7fV1d.png?sha=667b58a99791f774 - This happens in the **mitochondria**. - Kreb\'s cycle requires oxygen. - When a pyruvic acid loses CO~2~, it produces acetyl-CoA which oxidizes to form CO~2~, ATP, and other compounds (NADH and FADH~2~). ### **C. Oxidative phosphorylation**  - **Phosphorylation** is the process where electrons are combined with another molecule from the ATP. - The main goal is to transfer electrons from NADH and FADH2 to produce ATP. - The final electron acceptor in oxidative phosphorylation is the oxygen. The oxygen accepts the electrons to produce water within the mitochondrial matrix. - Two steps are involved: electron transport chain (**ETC**) and **chemiosmosis**. - **ETC** transports electrons but produces *no ATP*. - In **chemiosmosis**, ATP synthase is driven by protons to produce ATP. **Anaerobic Respiration** ------------------------- This occurs in the absence of oxygen and glucose is broken down to ATP. There are two types of anaerobic respiration: **alcoholic fermentation** and **lactic acid fermentation**. ### ### **A. Alcoholic Fermentation** - Glucose is converted to **alcohol**. This type of fermentation does not occur in humans. It usually occurs in bacteria and yeast. ### **B. Lactic Acid Fermentation** - This occurs in the human body when oxygen in the muscles is used up and the muscles still require more energy, thus producing **lactic acid**. This is especially evident during intense physical exercises or movements. **Key Points** - **Cellular respiration** is a process of energy conversion where carbohydrates are broken down into glucose and ATP. - There are two types of cellular respiration: **aerobic respiration** and **anaerobic respiration**. - **Aerobic respiration** occurs when glucose is broken down in the presence of oxygen. This has three stages: **glycolysis, Kreb\'s cycle,** and **oxidative phosphorylation**. - **Glycolysis** is a process by which glucose is broken down into pyruvic acids, ATP, and NADPH. - In **Kreb\'s cycle**, pyruvic acids produce acetyl-CoA to form CO~2~ and ATP. - **Anaerobic respiration** occurs in the absence of oxygen and glucose is broken down to energy. - Two types of anaerobic respiration: **alcoholic** and **lactic acid fermentation**. - In **alcohol fermentation**, glucose is converted to alcohol. - **Lactic acid fermentation** leads to the production of lactic acid in the human body when oxygen in the muscles is used up and still requires more energy. **Perpetuation of Life** **The Reproduction of Plants** **Angiosperms**, also called *flowering plants*, have seeds enclosed within an ovary while **gymnosperms** have unenclosed or \"naked\" seeds on the surface of their leaves or scales. **How do angiosperms and gymnosperms reproduce?** **Reproduction in Angiosperms** =============================== **Flowers** are the sexual reproductive organs in angiosperms. They consist of the **androecium** (male reproductive structure) and **gynoecium** (female reproductive structure). **Male Reproductive Parts of the Flower** ----------------------------------------- **Androecium** is the male reproductive structure of the plant that consists of a whorl of stamens. The **stamen** is comprised of the filament and the anther. The **filament** is a long, slender stalk that holds the anther while the **anther** produces the **pollen grains** (male reproductive cells). https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDYvMDYvMTcvMDQvNDgvMTc3ZjY3MjAtMDYzOC00OTlkLWI5ZTUtOTk3ZjA0YmRmYzA4L01hbGUlMjBSUC5wbmciXSxbInAiLCJ0aHVtYiIsIjYwMHhcdTAwM2UiLHt9XV0.png?sha=46570fb3a0d45461 \(a) Stamen\ (b) a cut section of the anther **Female Reproductive Parts of the Flower** ------------------------------------------- **Gynoecium** is the female reproductive structure of a flower. It may consist of a single pistil (monocarpellary) or may have several pistils (multicarpellary). The **pistil** is made up of the stigma, the style, and the ovary. The **style** is a slender stalk that supports the stigma while the **stigma** is the sticky part that receives the pollen. The **ovary** is the basal sac that contains the **ovules**(female reproductive cells). \  Both the male and female gametes of the flowers are non-motile. They are brought together by pollination. **Pollination** --------------- **Pollination** unites the male and female reproductive cells or gametes. It takes place when the pollen grains from the male anther are transferred to the female stigma. ### **Types of Pollination** - **Autogamy** is a type of pollination where pollen grains are transferred to the stigma of **the same** flower. - **Geitonogamy** is a type of pollination where pollen grains are transferred to the stigma of **another** flower of **the same** plant. - **Xenogamy**, also called *cross-pollination*, is a type of pollination where pollen grains are transferred to the stigma of a **different** plant. ### **Agents of Pollination** - **Abiotic agents** are nonliving things that aid in the transfer of pollen grains from the anther to the stigma. They include wind and water. - **Biotic agents** are living things that aid in pollination. They include animals and even humans. Example A bee, which sips nectar from flowers, transfers the pollen grains from one flower to another. It is an example of a biotic agent. Tips In pollination, the pollen grains are transferred to the female reproductive structures of a flowering plant. However, it does not guarantee the transfer of the correct type of pollen to another flower since the pollen grains are of the same species as the stigma where it came from. It is the pistil of the flower that recognizes whether the pollen is the correct type or not. If the received pollen is of the right type, the pistil recognizes and accepts the pollen to promote post-pollination events that lead to fertilization. **Fertilization** ----------------- **Fertilization** takes place when the sperm (germinated pollen) unites with the egg (ovule) forming a fertilized egg called a **zygote**. ### **Process of Fertilization** 1. The pollen grain attaches to the stigma. 2. Each pollen grain becomes a part of the pollen tube, which grows down the neck of the style and reaches the ovary. 3. Sperm cells are discharged into the embryo sac, fertilizing the egg cell. https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDYvMDYvMTcvMDYvMDgvYzA1OTgxMTUtNTIxOS00YmMxLWE4YWQtZDRhNmRjMmY3NTMxL0ZlcnRpbGl6YXRpb24ucG5nIl0sWyJwIiwidGh1bWIiLCI2MDB4XHUwMDNlIix7fV1d.png?sha=df18451cb8fe2f60 ### **Double Fertilization** During double fertilization, the pollen grain enters the ovary and releases **two sperm cells**. One sperm cell unites with the egg cell forming a diploid cell or zygote. The other sperm cell bonds with two polar nuclei forming a triploid endosperm nucleus. ### **Post-fertilization** During post-fertilization, the **zygote** develops into an **embryo** while the **endosperm nucleus** develops into the **endosperm**. Also, the **ovule**, which contains the embryo and endosperm, matures into a **seed** while the **ovary** forms the **pericarp** of the fruit. The seed is the beginning of the next generation. It grows into a seedling and then into a mature plant. The mature plant then produces flowers that contain the reproductive cells. **Reproduction in Gymnosperms** =============================== Unlike angiosperms, gymnosperms do not have flowers and fruits. Their ovules, which become seeds, are on the surface of a scale or modified leaf. Examples of gymnosperms include cycads and conifers. Most gymnosperms have reproductive parts called **cones**. They produce two kinds of cones: the male and the female cones. The **male cones produce the pollen** while the **female cones contain at least one ovule**. **Pollination** --------------- In gymnosperms, the main pollinating agent is wind. Wind carries the pollen from the male cones to the female cones. A sticky substance secreted by the ovule collects the pollen. **Fertilization** ----------------- After pollination, the ovule closes and seals in the pollen. One sperm cell fertilizes the egg cell forming a **zygote**. **Post-Fertilization** ---------------------- The fertilized egg develops into an embryo, and the other parts of the ovule mature into the seed coat and food store. **Key Points** - **Angiosperms** have seeds enclosed within an ovary while **gymnosperms** have unenclosed or \"naked\" seeds on the surface of their leaves or scales. - The flower consists of the **gynoecium** (female reproductive structure) and **androecium** (male reproductive structure). - Most gymnosperms have reproductive parts called **cones**. The male cones produce the pollen while the female cones contain at least one ovule. - **Pollination** unites the male and female reproductive cells or gametes. - **Fertilization** is the union of pollen grain and ovule in the ovary. - During **double fertilization**, one sperm cell fertilizes the ovule forming the zygote (diploid) while the other sperm cell unites with the two polar nuclei to form the endosperm (triploid). - In **angiosperm fertilization**, the zygote matures into an embryo while the rest of the ovule develops into a fruit. - In **gymnosperm fertilization**, the zygote matures into an embryo while the rest of the ovule develops into a seed. **The Reproduction of Animals** Animals produce sounds which are significant in their reproduction. It is an essential feature of living organisms because, without reproduction, life will not exist. **How do different animals ensure continuity of species?** There are two types of reproduction that exists in living organisms: asexual and sexual reproduction. **Asexual reproduction** is common among lower form of animals while **sexual reproduction** can be found in more complex animals. \  **Asexual Reproduction** ------------------------ This type of reproduction does not need two parents to produce an individual. Therefore, the offspring produced is the exact copy of the parent animal. Most common forms are fission, fragmentation, and budding. ### **Fission** **Fission** is a type of asexual reproduction wherein two individuals will form as the parent divides in half. The illustration below shows a sea anemone undergoing fission.\ Fragmentation **Fragmentation**, the breaking of body parts into fragments, is always followed by regeneration and regrowth of lost parts. Even if the animal is broken into many pieces, each piece will grow into a new individual. Planarians, as shown in the illustration below, as well as sponges, cnidarians, bristle worms, and sea squirts reproduce by fragmentation.\ https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDUvMTIvMTUvNDAvMDgvZDg4OGMwN2UtOGNkOS00YmY3LWFiN2YtOWVkODUwZWViZmQ1L2ZyYWdtZW50YXRpb24ucG5nIl0sWyJwIiwidGh1bWIiLCI2MDB4XHUwMDNlIix7fV1d.png?sha=e61b3588cc129743 ### **Budding** **Budding** is when an outgrowth called a **bud** grows and develops from the parent animal and would eventually separate to become a new individual. This type of reproduction is common in certain species of coral and hydra.\  **Sexual Reproduction** ----------------------- Sexual reproduction needs two parents to produce an offspring. The combination of the genes from both parents increases the chances of species variation. Therefore, species extinction is highly unlikely. Fertilization, the union of egg and sperm cells, could happen internally or externally. ### **External Fertilization** In external fertilization, the union of egg and sperm occurs outside the female reproductive tract. This is common among most species of bony fish and amphibians. As shown in the illustration below, the clasping of the male frog induces the female to release eggs, over which the male releases his sperm. \ https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDUvMTMvMTAvMjEvMzQvM2RlMmQzYTYtMGQ2YS00MGVjLWJiNTItNzdmMGFlNGVjYWNhL2V4dGVybmFsJTIwZmVydGlsaXphdGlvbi5wbmciXSxbInAiLCJ0aHVtYiIsIjYwMHhcdTAwM2UiLHt9XV0.png?sha=2e0363a6d9461e98\ Most eggs of the amphibians develop in the water but others carry them on their back or in their vocal sacs as shown below.\  ### **Internal Fertilization** In **internal fertilization**, the union of egg and sperm occurs within the female reproductive tract. Animals that undergo in this type of reproduction produce offspring in any of the following ways: oviparity, ovoviviparity, and viviparity. - **Oviparity** -- after the eggs are fertilized internally, it would complete its development outside the mother's body. The egg would receive its nourishment through its yolk. This is found in some bony and cartilaginous fish (including clown fish and blue tangs), most reptiles, some amphibians, all birds, and a few mammals (monotremes). - **Ovoviviparity** -- the eggs are also fertilized internally and receive its nourishment through its yolk. However, eggs will complete its development within the mother. They are then fully developed when they are hatched and released by the mother. This is common in some bony fish (including mollies, guppies, and mosquito fish), some cartilaginous fish, and many reptiles. - **Viviparity** -- the eggs are developed internally and receive nourishment directly from the mother's blood through placenta rather than from the yolk. This can be found in most cartilaginous fish (including lemon sharks), some amphibians, a few reptiles, and almost all mammals including humans. Explore! Jellyfish reproduction involves both sexual and asexual reproduction. Sexual reproduction occurs in the adult stage where males release sperm and females release eggs. When sperm and egg combine, it will form a small larva called planula. These planulae will attach to rocks and become polyps. During this stage, they can reproduce asexually by elongating then budding off to produce many young jellyfish. \ Why do you think many species of jellyfish produce offspring extraordinarily quickly? **Key Points** - **Reproduction** is an important feature of living organisms because it ensures continuity of species. - The two types of reproduction that exist in living organisms are asexual and sexual reproduction. - **Asexual reproduction** involves only one parent to produce a new individual. The offspring is the exact copy of the parent animal. Most common forms are fission, fragmentation, and budding. - **Fission** is a type of asexual reproduction wherein two individuals will form as the parent divides in half. - **Fragmentation** involves the breaking of body parts into fragments. Each piece will regenerate and become a new individual. - **Budding** is when a bud grows and develops from the parent animal then would eventually separate to become a new individual. - **Sexual reproduction** needs two parents to produce an offspring. The combination of the genes from both parents increases the chances of species variation. - **Fertilization** could happen internally or externally. - **External fertilization** involves the union of egg and sperm outside the female reproductive tract. - **Internal fertilization** involves the union of egg and sperm within the female reproductive tract. Animals that undergo in this type of reproduction produce offspring in any of the following ways: **oviparity**, **ovoviviparity**, and **viviparity**. **DNA: Its Role in Inheritance and Protein Synthesis** **What do you observe in this diagram?** https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDYvMDcvMDYvMzIvNTYvZWI3NjMwYjAtOWI3NC00ZDEwLWI5MDMtYTNlZTkzNDQyMzUxL1JlY2lwZS5wbmciXSxbInAiLCJ0aHVtYiIsIjYwMHhcdTAwM2UiLHt9XV0.png?sha=1dbe0668135cf1e8 Deoxyribonucleic acid (**DNA**) contains the genetic information of almost all living organisms. It contains **nucleotides**composed of a five-carbon sugar deoxyribose and a phosphate group. There are four nucleotides in a DNA: **adenine** (A), **thymine** (T), **guanine** (G), and **cytosine** (C). \  The **nucleic acid sequence** indicates the order of nucleotides in a DNA or RNA strand. The nucleotides or nucleotide bases (A, C, T, G) of a DNA strand or a sequence can be complementary to another sequence. Cytosine pairs with guanine, and adenine pairs with thymine in the complementary DNA strand. The sequence of the DNA strand contains codes of information that provide instructions for making proteins needed by organisms in order to grow and live. In our diagram in the previous lesson chapter, the recipe was transcribed into English for one to make the recipe. The same with DNA, if not transcribed, it will not give instructions to make proteins needed by our cells. **Role of DNA in Inheritance** ------------------------------ **Genes** are short segments of DNA that are the basic units of heredity. Every individual has two copies of each gene, one from the father and the other from the mother. They are responsible for all the traits that an individual inherits from their parents. The sperm and egg cells carry 23 chromosomes each. When they unite, a total of 46 chromosomes will be produced. The only thing that makes us unique from each other is the slight variations in the genes. For example, most of us have black eyes, some have brown eyes. We all have genes for eye colors, but the differences in the genes dictate whether a person will have black or brown eyes. **Role of DNA in Protein Synthesis** ------------------------------------ The DNA plays an important role in the synthesis of proteins. **Proteins** play an important role in the cells' functions and structures. There are three processes involved in the production of proteins: **replication, transcription,** and **translation**. ### ### **Replication** **Replication** refers to the process of copying one DNA to produce two identical DNA molecules. During this process, the DNA unwinds, and both strands of the double helix will serve as templates for producing new strands of DNA. https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDYvMDcvMDYvMzMvNTIvMTMzYjg0NjYtYjE2NS00NDNmLTllZGYtYzhjMWQ0MjgzNDUxL0ROQTIucG5nIl0sWyJwIiwidGh1bWIiLCI2MDB4XHUwMDNlIix7fV1d.png?sha=bada5b85c7fdbeaf ### **Transcription** **Transcription** is the process by which the genetic information in the DNA strand is transcribed to the messenger RNA (**mRNA**). This RNA is called the messenger RNA because it carries the message copied from the DNA to produce proteins. In this process, RNA uses complementary coding where the bases are matched up, similar to how DNA forms a double helix. The difference between RNA and DNA is that instead of thymine, RNA makes use of **uracil**.  ### **Translation** **Translation** is the process wherein protein molecules are assembled from the information encoded in mRNA. As a whole, the synthesis of proteins is made possible by the DNA which provides the information needed to create proteins in the body. https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDYvMDcvMDYvMzQvMzUvNDllMjEwOGMtOTI0NC00MmVmLWIxZDYtZDc4ZWZjNmRmMTQ0L3RyYW5zbGF0aW9uLnBuZyJdLFsicCIsInRodW1iIiwiNjAweFx1MDAzZSIse31dXQ.png?sha=24e3b0da747fdcc1 **Key Points** - **DNA** contains the genetic information of almost all living organisms. - The **nucleotide** consists of deoxyribose and a phosphate group. - There are four nucleotides in a DNA: **adenine** (A), **thymine** (T), **guanine** (G), and **cytosine** (C). - **Genes** are short segments of DNA that are the basic units of heredity. - **Replication** refers to the process of copying one DNA to produce two identical DNA molecules. - **Transcription** is the process by which the genetic information in the DNA strand is transcribed to the messenger RNA (mRNA). - **Translation** is the process wherein protein molecules are assembled from the information encoded in mRNA. **Genetic Engineering and Its Applications in Reproduction** **Have you ever heard of genetically modified organisms?** **Genetic Engineering and Biotechnology** ========================================= **Genetic engineering** means modifying genes in a living organism to produce genetically modified organisms (GMOs) also known as **transgenic organisms**. It is a modern type of genetic modification. In this process, the **gene of interest** is physically removed and placed in an organism to be modified. This method is more rapid and specific than the traditional plant breeding because a gene coding for a specific trait could be transferred to an organism. Genetic engineering is an application of **biotechnology** which uses biological systems, processes, or organisms to create products intended to improve the quality of human life. **How is genetic engineering done?** ------------------------------------ \ As shown in the illustration above, copies of the **recombinant plasmid**--- a circular, double-stranded DNA molecule, will be isolated and transferred to other organisms. Depending on the gene of interest, genetic engineering has various applications in the field of medicine, environment, and agriculture. To help you describe the processes involved in genetic engineering, let us use Bt corn, a genetically modified pest resistant plant as an example. This plant was grown in the Philippines against Asian corn borer, a major pest in corn. **DNA Isolation (isolating plasmid and gene of interest)** The first step in creating a pest-resistant plant is isolating the plasmid of *Agrobacterium* and pest- resistant gene from a bacteria, *Bacillus thuringiensis* (Bt). \ https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDUvMTMvMDMvMTAvMzcvMTY0ZWM5ZTItZmIzYy00ZDNiLTg1NmQtZDg2MTIxYmI0YTIyL0ROQSUyMGlzb2xhdGlvbi5wbmciXSxbInAiLCJ0aHVtYiIsIjYwMHhcdTAwM2UiLHt9XV0.png?sha=86afb67750336426 - ***Agrobacterium tumefaciens***, a gram-negative soil bacteria cause crown gall disease in plants but its tumor-inducing plasmid is usually used in genetic engineering because of its ability to integrate its DNA into a plant's genome. - The resistant gene would be obtained in the DNA of ***Bacillus thuringiensis***. This bacterium produces a protein known as *Cry1Ab toxin* that is lethal to the larval stage of **lepidopterans** (moth family). **Ligation (gene insertion to the plasmid)** When the resistant gene is inserted into the isolated plasmid, they are cleaved using the same restriction enzyme before they are combined using DNA ligases. **Restriction enzymes** are also called **restriction endonucleases**. Once they recognize a specific nucleotide sequence, they cleave the strands. \  **Transformation (plasmid is placed back into bacterial cell)** The recombinant plasmid would then be placed back to the bacterium in a process called **transformation**. \ https://d14fikpiqfsi71.cloudfront.net/media/W1siZiIsIjIwMTYvMDUvMTMvMDMvMjgvNTEvYjliODVhMjQtNzk1YS00YTE5LTgyZWQtMTA5NWEyMzhmMTg2L3RyYW5zZm9ybWF0aW9uLnBuZyJdLFsicCIsInRodW1iIiwiNjAweFx1MDAzZSIse31dXQ.png?sha=24cb3d39699700ff **Selection (identification of the desired clone)** The nutrient media with **X-gal** (special galactose sugar) are used to select the transformed bacteria containing the recombinant plasmid with the gene of interest. The selected bacteria would then infect the cell of corn and integrate the gene into the plant's DNA. When the plant cell divides, each daughter cell receives the new gene. The transformed corn plant is now pest-resistant.  The inserted gene producing the toxin in the genetically modified crop is only lethal to specific target pests. **Current Uses of GMOs** ======================== The genes of bacteria, plants, and animals are being modified to improve the quality of human life. Depending on the gene of interest, GMOs have many uses in agriculture, medicine, and the environment. **Uses of Genetically Modified Bacteria** ----------------------------------------- - ***Escherichia coli*** creates a synthetic human insulin. - **Cyanobacteria** is used to yield polyhydroxybutyrate to produce bioplastic. **Uses of Genetically Modified Plants** --------------------------------------- - **Bt corn** is a pest-resistant plant against corn-infesting larvae. - **Banana vaccine** is an edible vaccine against hepatitis virus. - **Golden rice** is a genetically modified rice that produces beta-carotene. **Uses of Genetically Modified Animals** ---------------------------------------- - **Bioluminescent animals** are used to identify different types of cells to detect diseases. - Some bioluminescent animals such as glofish became novelty pets to humans. - **Fast-growing salmon** are genetically modified salmon to continually produce growth hormones. **Advantages of GMOs** ====================== The GMOs offer many benefits to mankind such as: - **Increased productivity.** This enables farmers to have higher crop yields and reduced pesticide use. (e.g. Bt corn) - **Reduced pesticide use.** Since GM crops are modified for a specific pest, the use of pesticide against that pest is reduced or removed. - **Improved nutrition like the high beta carotene content of Golden Rice.** GM crops such as Golden Rice with improved nutrition (high in beta carotene) reduces eye-related problems like blindness due to malnutrition. - **Aided disease detection.** Diseases can be identified because of protein trackers in bioluminescent animals. **Disadvantages of GMOs** ========================= GMOs also raised concerns from people because of its possible harm to the environment and mankind such as: - **Reduced biodiversity of non-damaging insects.** Pest resistant crops (e.g. Bt corn) lead to unintended harm to non-crop damaging insects such as larvae of Monarch butterflies when affected by pollen of Bt corn. - **Decreased pesticide effectivity.** Pest resistant crops seem to reduce the need for pesticide at first but it would increase later on. - **Produced allergic reactions.** Some people develop an allergic response to GM crops when exposed to them. - **Led to a higher cost for GM seeds.** Farmers buy new seeds every year. Farmers using second generation seeds would lead them to Supreme Court with a charge of patent infringement. **Key Points** - **Genetic engineering** means altering genes in a living organism to produce a Genetically Modified Organism (GMO). - **Biotechnology** is a technology using biological systems, processes, or organisms to create products intended to improve the quality of human life. - The following are the steps in genetic engineering: DNA isolation, ligation, transformation, and selection. - **DNA isolation** is isolating the plasmid and gene of interest. - **Ligation** involves sealing the gene of interest into the plasmid after they are both cut with the same restriction enzyme. - **Transformation** is a process wherein cells ingest foreign DNA from the surroundings. - **Selection** is the process where the bacteria containing the recombinant plasmid with the gene of interest is selected and will be used to integrate the gene of interest in the host organism. - Depending on the gene of interest, GMOs have many uses in agriculture (e.g. pest resistant plants), medicine (e.g. edible vaccines), and environment (e.g. butanol production). - GMOs offer many benefits to mankind such as increased productivity, improved nutrition, disease detection, and cheaper medicines. - Possible risks about GMO such as reduced biodiversity, decrease pesticide effectivity, allergic reactions, and high cost for GM seeds posed concerns to many people. **Animal Survival, Earth and Life Science** **Nutrient Absorption in Cells** **How are nutrients absorbed inside the body?** The nutrients that the body needs come from food. These nutrients are absorbed by the body during digestion. **Digestion** is the process by which food is broken down into simple, soluble compounds in the digestive tract. It involves mechanical and chemical processes. 1. **Mechanical Process** - During the mechanical process, the food is broken down into small particles that are mixed with the digestive juices. This process starts in the mouth and continues into the stomach. 2. **Chemical process** - During the chemical process, also known as **hydrolysis**, digestive enzyme changes food particles into soluble forms that can be easily absorbed. For example, enzymes change carbohydrates into simple sugars, proteins into amino acids, and fats into fatty acids and glycerol. The chemical process starts in the mouth and continues into the small intestine. After the food undergoes mechanical and chemical processes, the nutrients are absorbed in the small intestine and into the bloodstream. Then they are passed to different cells where they are used in metabolic processes. For instance, the liver cells contain enzymes which use the nutrients to form complex molecules. ### Absorption **Absorption** is the passage of nutrients through the intestinal walls and into the blood. The primary site of absorption is the **small intestine**. The **villi**, which are tiny finger-like projections, trap the nutrients which are taken in by the adjacent cells. The **capillaries**, tiny blood vessels contained in the villi, serve as the passageway for the nutrients to reach the general blood circulation. These nutrients are carried by the blood to the liver and from there, distributed to various organs and tissues. The body is able to digest and absorb about 90% to 98% nutrients of a mixed diet. ### Metabolism **Metabolism** is a process that converts absorbed nutrients into energy needed for repair, growth, and development of organisms. All types of metabolism happen at the cellular level, specifically **intracellular** or inside the cell. When metabolism results in building new substances, it is called **anabolism**. If the nature of metabolism is destructive, it is called **catabolism**. Numerous complex biochemical changes occur within the cells through anabolic and catabolic processes. When the cells in the body need energy, a series of catabolic reactions occur. Catabolism happens in the **mitochondria**, which act as a \'furnace\' that burns food energy. The presence of oxygen is necessary for the release of energy by the cells. The process of combining oxygen to a molecule is called **oxidation**. The figure below shows what happens to carbohydrates, fats, and proteins as they undergo catabolic processes. As they undergo digestion and absorption, soluble forms of food are converted to energy in the form of adenosine triphosphate (ATP). ATP is often called the energy currency molecule of the cells. C:\\Users\\ACER\\Desktop\\SHS11-12\\1.Earth and Life Science\\2nd Quarter Earth & Life\\SCI (Life Science) Absorption of Nutrients.png ### Carbohydrates Carbohydrates can be converted to usable energy through glycolysis. **Glycolysis** is an anaerobic process (does not require oxygen) that happens in the cytosol. This process converts glucose into pyruvates while producing a small amount of energy. After glycolysis, the pyruvates pass through the cytosol and goes into the mitochondria. When the cells need energy, aerobic reactions (require oxygen) occur in the mitochondria. Each molecule of pyruvate is converted into acetyl-CoA molecule. The acetyl-CoA enters the Kreb\'s cycle, which generates ATP. Overall, the complete breakdown of glucose yields to carbon dioxide, water, and ATP. ### ### ### Fats Fats can be converted into energy through beta-oxidation. **Triglycerides**, the dietary form of fat, are first broken down into fatty acids and glycerol. **Fatty acids** contain almost all the energy found in triglycerides. Their breakdown occurs in the mitochondria. To enter the mitochondria, they are first activated through linking with coenzyme A. Carnitine then transports the activated fatty acids across the mitochondrial membrane. Once the fatty acids reach the mitochondria, a process called **beta-oxidation** strips up the fatty acids and converts them to molecules of acetyl-CoA. The acetyl-CoA enters the Kreb\'s cycle. The complete breakdown of fatty acids yields carbon dioxide, water, and ATP. ### Proteins Proteins are not the major sources of energy. However, when there are no carbohydrates and fats available for energy production, proteins can be the alternative source. During the **starvation state**, the body breaks down protein and extracts the energy needed by the body from the amino acids. To use amino acids as a source of energy, they must undergo the process of **deamination**. In this process, the amino group (-NH) is stripped off, leaving the \"carbon skeleton\". The carbon skeleton is used by the liver to produce energy. The type of amino acid where the carbon skeleton came from determines whether it would be converted to pyruvate, acetyl-CoA, ketone body, or other intermediates of the Kreb\'s cycle. The breakdown of the amino acid yields urea, carbon dioxide, water, and ATP. **Key Points** - **Absorption** is the passage of nutrients through the intestinal walls and into the blood. The primary site of absorption is the **small intestine**. - Absorbed nutrients are carried by the blood to the liver and from there, distributed to various organs and tissues as needed. - **Metabolism** is a process that converts absorbed nutrients into energy needed for repair, growth, and development of organisms. - When metabolism results in building new substances, it is called **anabolism**. - If the nature of metabolism is destructive or oxidative and release heat and energy, it is called **catabolism**. - **Glycolysis** is an anaerobic process that converts glucose into pyruvates used in the Kreb\'s cycle to produce energy. - **Beta-oxidation** strips up the fatty acids and converts them to molecules of acetyl-CoA which enters the Kreb\'s cycle to complete the extraction of energy from fatty acids. - **Deamination** is the process where the amino group (-NH) is stripped off, leaving the \"carbon skeleton\" that is converted to pyruvate, acetyl-CoA, ketone body, or other intermediates of the Kreb\'s cycle. - The breakdown of glucose, fatty acids, and amino acids yield carbon dioxide, water, and ATP. **Gas Exchange of Organisms** Animals have respiratory structures that enable them to breathe in oxygen that is delivered to their cells. For instance, mammals have lungs for gas exchange. **Have you ever wondered how other animals such as fish, insects, frogs, earthworms, and turtles breathe?** **Gas exchange** in animals refers to the exchange of respiratory gases -- uptake of molecular oxygen and discharge of carbon dioxide. This process follows the principle of **diffusion**, the movement of molecules from an area of high concentration to one of low concentration. Animals have different respiratory structures used for gas exchange. Important respiratory structures include the gills, the tracheal system, the skin, and the lungs. ### Gills Fish and other aquatic animals have gills that are used to take in dissolved oxygen in water. When the oral valve in their mouth opens, it draws the water into the **buccal cavity**. The **opercular cavity**, where the gills are housed, then closes. When the oral valve closes, the **operculum** (gill cover) opens to move out the water through the gills.  In the gill filament, the blood in the capillaries flows in a direction opposite to the water flow. This opposite flow allows for **countercurrent exchange**, the exchange of materials between two fluids flowing in opposite directions. As a result, the oxygen molecules diffuse from water (higher O2 concentration) to the blood (lower O2concentration). This mechanism maximizes gas exchange efficiency because if both fluids flow in the same direction, the concentration difference will decrease rapidly. ### ### Tracheal System The tracheal system is common in insects. This system does not need the direct participation of the circulatory system to transport O2 and CO2 since the air can diffuse directly to the cells. C:\\Users\\ACER\\Desktop\\SHS11-12\\1.Earth and Life Science\\2nd Quarter Earth & Life\\SCI (Life Science) Tracheal System.png In every segment of the insect's abdomen, there are pairs of openings called **spiracles**, where air enters and leaves the body. These openings connect to the tubular network called **trachea** that eventually branches into **tracheoles**. When the oxygen reaches the tracheoles, it diffuses into the cytoplasm of a nearby body cell. On the other hand, CO2, which is formed as waste product, diffuses out of the cell and eventually out of the body through the tracheal system. Another part of the tracheal system is the **air sac** which serves as an air reservoir. ### Skin Amphibians, earthworms, and some turtles can breathe through their skin in a process called **cutaneous respiration**. They respire through their skin when they are submerged in water or damp areas. It is important for them to keep their skin moist to allow efficient cutaneous respiration. To avoid desiccation, their skin secretes mucus through the **mucus glands**. Cutaneous respiration also occurs through **concurrent exchange**, where the direction of the absorbed oxygen is directly opposite the circulation of the blood in the skin. Tip Though many amphibians can breathe through their skin in water, note that they also have lungs that they use for breathing on land. **Lungs** The lungs are the primary organs of respiration in mammals. During respiration, the air has to go through different organs before reaching the lungs. When air is inhaled, it passes through a windpipe called **trachea**. The trachea then divides the air into air passages called the **bronchial tubes** or **bronchi** located at the lungs. Upon reaching the lungs, the air passes through smaller airways called the **bronchioles** with tiny balloon-like air sacs called the **alveoli**at their ends. **Capillaries**, a network of tiny blood vessels, surround the alveoli. These vessels are the sites of gas exchange. After the deoxygenated blood in the capillaries absorbs the oxygen from the **alveoli walls**, it travels to the heart which in turn, pumps it throughout the body to provide oxygen to the cells. On the other hand, CO2produced by the cells is carried by the blood back to the lungs where it is removed through exhalation.  **Key Points** - **Gas exchange** refers to the uptake of oxygen from the environment and discharge of carbon dioxide. - **Diffusion** is the principle involved in gas exchange. It is the movement of molecules from an area of high concentration to one of low concentration. - Different respiratory structures are found in the different animals. - **Gills** are the organs that enable fishes and other aquatic animals to breathe in oxygen dissolved in water and excrete carbon dioxide. - **Tracheal system** is common in insects. This system is composed of the spiracles, the trachea, the tracheoles, and the air sacs. - **Cutaneous respiration** is breathing through the skin. It is common in amphibians and some turtles. - **Lungs** are common in mammals. Capillaries located in the alveoli are the sites of gas exchange. **Nutrient and Waste Transport System** **What are the different organs involved in the nutrient and waste transport in the body?** ### Main Transport System The main transport system for animals is the circulatory system. The **circulatory system** plays a central role in an organism's survival. The **human circulatory system** comprises of the **heart**, the **blood**, and a closed system of structures called **blood vessels** which include the arteries, the veins, and the capillaries. The main functions of the circulatory system are to distribute the nutrients and oxygen to all body cells and transport waste products to the liver, kidneys, and lungs. This system works through **diffusion**---the movement of molecules from an area of high concentration to an area of low concentration. However, diffusion only occurs over short distances such as between blood and air in the lungs. In terms of the distribution of blood throughout the human body, the process of bulk flow takes place. **Bulk flow** is the movement of the blood from an area of high pressure to an area of low pressure through the action of the heart that pumps the blood and pressurizes it to flow. This process allows a rapid transport of blood in all parts of the body. ### Components of the Circulatory System **The Heart** The **heart** is the muscle that pumps blood throughout the body. It consists of four chambers. The top two chambers are called **atria** while the bottom two are called **ventricles**. The **atria** are the receiving chambers for blood returning to the heart. The blood from the circulation enters the right atrium while the reoxygenated blood from the lungs enters the left atrium. The atria are thin-walled chambers because they need to contract only minimally to squeeze blood into the ventricles. In contrast, the **ventricles** have thicker walls because they need to contract harder to pump blood out of the heart and into the circulation. The right ventricle pumps blood into the pulmonary trunk while the left ventricle ejects blood into the aorta. The delivery system of the heart is separated into two circuits: the pulmonary and the systemic circuits. The **pulmonary circuit**, supplied by the right side of the heart, receives the returning blood and pumps the blood to the lungs for reoxygenation and dispatch of carbon dioxide. On the other hand, the **systemic circuit**, supplied by the left side of the heart, transports the oxygenated blood to the entire body. **The Blood Vessels** **Blood vessels** are responsible for the transport of blood throughout the body. There are three types of blood vessels: arteries, veins, and capillaries. **Arteries** carry oxygenated blood away from the heart while **veins** carry deoxygenated blood towards the heart. **Capillaries** are tiny, thin-walled vessels that allow water, nutrients, and oxygen from the blood to move to the surrounding tissues and allow wastes to move out in the opposite direction.  **The Blood** The **blood** is a special connective tissue that distributes essential nutrients, including oxygen while collecting wastes, such as carbon dioxide. It consists of a yellowish fluid called **plasma**, which contains red blood cells, white blood cells, and platelets. The **red blood cells** have **hemoglobin**, the protein that transports oxygen to the different tissues in the body. This protein also releases the carbon dioxide picked up from body tissues. ### The Path of the Circulatory System The deoxygenated blood passes through the right side of the heart which pumps it into large vessels called **pulmonary arteries**. It then moves into the lungs where it is \'cleaned\' as the carbon dioxide is exchanged with oxygen. This process of exchange between the carbon dioxide and oxygen is called **oxygenation**. The oxygenated blood travels back into the heart through the pulmonary veins. The oxygenated blood is pumped into the largest blood vessel and the main artery in the human body called **aorta**. Before the blood leaves the aorta, it passes through the small arteries. Then finally, it passes through the capillaries which distribute it to all the tissues of the body. Oxygen and nutrients are delivered to these tissues. Simultaneously, the waste products of the cells are carried away by the blood. As soon as all the oxygen is used up, the blood goes into the veins and travels back into the heart. ### Closed and Open Circulatory Systems Humans have closed circulatory system. In a **closed circulatory system**, the circulatory fluid or blood is limited within vessels. The heart pumps blood into large vessels, branching into smaller vessels and into different organs. Other animals with closed circulatory system include squids and earthworms. On the other hand, in an **open circulatory system**, the circulatory fluid called **haemolymph** coats the body cells. The heart pumps the haemolymph through circulatory vessels and goes into the sinuses or the spaces surrounding the organs. Arthropods such as grasshoppers have open circulatory systems. **Key Points** - The main transport system for animals is the circulatory system. - The **circulatory system** plays a central role in an organism's survival and is interconnected with the **respiratory system**. - The **heart** is the muscle that pumps blood throughout the body. - The delivery system of the heart is separated into two circuits: the pulmonary and the systemic circuits. - The **pulmonary circuit** receives the returning blood and pumps the blood to the lungs for reoxygenation and dispatch of carbon dioxide. - The **systemic circuit**, supplied by the left side of the heart, transports the oxygenated blood to the entire body. - **Blood vessels** are responsible for the transport of blood throughout the body. - There are three types of blood vessels: arteries, capillaries, and veins. - **Arteries** carry oxygenated blood away from the heart. - **Capillaries** are tiny, thin-walled vessels that allow water, nutrients, and oxygen from the blood to move to the surrounding tissues and allow wastes to move out in the opposite direction. - **Veins** carry deoxygenated blood towards the heart. - The **blood** is a special connective tissue consisting of cells surrounded by a fluid called plasma. - The **plasma** is a yellowish liquid and considered as the biggest component of the blood. - **Red blood cells** carry oxygen to the different tissues in the body and pick up carbon dioxide to be eliminated. - In a closed circulatory system, the heart pumps blood into large vessels, branching into smaller vessels and into different organs. On the other hand, in an open circulatory system, the heart pumps the circulatory fluid called hemolymph through circulatory vessels and goes into the sinuses. **Homeostasis** **How does the human body maintain homeostasis?** **Homeostasis** **Homeostasis** comes from the two Greek words *homeo* meaning similar and *stasis* meaning stable. It is the ability of the body to maintain a constant internal equilibrium. It keeps the body functioning well even when there are changes in the environment. Examples of homeostasis include the regulation of body temperature, blood sugar level, and blood urea level. Although homeostasis maintains a constant internal balance, it is not a static state. It is a dynamic state or continuously changing. Take the body temperature as an example. Humans generate internal body heat and maintain an average temperature of about 37˚C. However, the body temperature still varies all throughout the day. During daytime, especially when doing physical activities, the body temperature rises. At nighttime, the temperature slightly falls during sleep. Homeostasis is achieved through automatic mechanisms. These mechanisms have at least three interdependent components. The components are the receptor, control center, and effector. - The **receptor** is a sensing component that monitors changes in the external or internal environment. For example, peripheral chemoreceptors detect changes in the pH of the blood. - The **control center** receives messages from the receptors and initiates the response to maintain homeostasis. The **brain** is the control center of the human body. The brain responds by sending signals in the form of nerve impulses to other organs (effectors) to bring about changes needed to maintain homeostasis. For example, hypothalamus is ta part of the brain that receives signals when there are changes in the blood pressure and heart rate. - The **effector** is an organ or tissue that receives the messages from the control center and brings about changes needed to maintain homeostasis. For example, the organs of the endocrine system act as effectors that release hormones into the blood to correct any disruptions. ### Types of Feedback Mechanism Homeostasis is maintained through feedback mechanisms, which are series of events in which the condition of the body is strictly and constantly monitored, evaluated, and changed. **Negative Feedback Mechanism** **Negative feedback mechanism** occurs when the change in the body, caused by stimuli, reverses as a response of a particular effector. An example is the control of the blood sugar by the hormones insulin and glucagon which are both secreted by the pancreas. **Insulin** is secreted when the blood sugar level is high while **glucagon** is secreted when the blood sugar is low. When the blood sugar increases, the hypothalamus sends signals to the pancreas to secrete insulin into the bloodstream and lower the blood sugar level. When the blood sugar level reaches equilibrium, the pancreas stops the release of insulin. On the other hand, when the blood sugar level is low, the hypothalamus sends signals to the pancreas to secrete glucagon and increase the blood sugar level. **Positive Feedback Mechanism** **Positive feedback mechanism** occurs when the changes are strengthened by the response of the effector. It occurs when the changes enhance the effect of the stimulus. For example, the pituitary gland secretes oxytocin during childbirth as a positive feedback mechanism. Oxytocin intensifies and speeds up the contraction in the mother's womb. Increase in contractions hastens the delivery of the baby. After giving birth, the production of oxytocin stops. Another example of a positive feedback is **lactation**, which is the production of milk in the mammary glands. The suckling action of the baby triggers the pituitary glands to produce prolactin, which stimulates milk production. More suckling leads to an increase in prolactin, which in turn leads to more lactation. **Key Points** - **Homeostasis** is the ability of the body to maintain internal equilibrium in response to changes in the environment. - Examples of homeostasis include: - the regulation of body temperature; - the regulation of water balance in the blood; - the regulation of blood sugar level; and - the regulation of blood urea level. - The **feedback system** is a series of events in which the condition of the body is strictly and constantly monitored, evaluated and changed. - **Negative feedback mechanism** occurs when the change in the body, caused by stimuli, reverses as a response of a particular effector. - **Positive feedback mechanism** occurs when the changes are strengthened by the response of the effector. **The Immune System: Defense for Diseases** **How does the human body fight against harmful microbes?** The **immune system** is a collection of cells, organs, and processes that protect the body against foreign substances that can cause certain diseases. **Immunity** is the body's ability to fight certain illnesses, damages, and diseases caused by microbes. **Parts of Immune System** 1. The **bone marrow** is responsible for the production of different types of white blood cells which provide defense against infections. 2. The **lymph nodes** are structures that analyze destroyed cells and find molecules called **antigens** which stimulate an immune response, such as activating white blood cells. 3. The **spleen** acts as a large lymph node capable of destroying and segregating malfunctioning cells as well as old cells. There are two basic types of immunity: the innate immunity and adaptive immunity. **Innate immunity** provides immediate actions to protect the body against pathogenic microbes and other toxins. This type of immunity is the first line of defense in the body. It treats all microbes in the same way. **Cells involved in innate immunity response:** - **Macrophages** are white blood cells that engulf cell debris, bacteria, and viruses by the process known as **phagocytosis**. - **Neutrophils** are white blood cells that are smaller than macrophages, but they can also engulf viruses and bacteria. - **Mast cells** are abundant in connective tissues. They can mediate inflammatory responses, such as allergic reactions and hypersensitivity. - **Dendritic cells** are specialized cells which serve as messengers between innate and adaptive immune response by processing antigens to be recognized by the lymphocytes.  **Adaptive immunity** refers to a highly specific mechanism of the immune system that recognizes a particular pathogenic microbe. This type of immunity provides a long-lasting protection because it has the ability to remember its actions to a particular antigen. **Cells involved in adaptive immune response:** - **Lymphocytes** are specialized white blood cells that determine the specific response of the immune system to a particular infection. - Specific lymphocytes called **B-lymphocytes** are able to produce antibodies that destroy foreign substances while other lymphocytes called **T-lymphocytes** can recognize, respond, and recall (immune memory) antigens. ***What is the relationship between the innate and the adaptive immune response?*** When the infection passed the first line of defense provided by the innate immune system, the cells involved in adaptive immune system will take their place and attack the invaders. Innate immune response includes dendritic cells which are very efficient in presenting antigens that can interact with adaptive immune response specifically with T-lymphocytes. ***What happens when the immune system fails to function?*** Disorders in immune system such as AIDS, allergies, and autoimmune disorder will develop if there is an appropriate response created by the body either to a typical substance in the environment or to a component of the body in case of autoimmune diseases. **Key Points** - The **immune system** is a collection of cells, organs, and processes that protect our body against foreign substances that can cause certain diseases. - The two basic types of immunity are the **innate immunity** and **adaptive immunity**. - The cells involved in the innate immune system are macrophages, neutrophils, mast cells, and dendritic cells while lymphocytes belong to the adaptive immune system. **Hormones: The Chemical Messengers** **How can hormones affect the activities of the body?** **Hormones** are organic substances released by the glands of the **endocrine system** directly into the bloodstream. The hormone-releasing glands are the pineal gland, hypothalamus, pituitary gland, thyroid, thymus, pancreas, adrenal, testicle, and ovary. Hormones are capable of changing the physiological and metabolic behavior of their target cells to maintain homeostasis. **Types of Hormones Based on Chemical Structures** **Peptide and protein hormones** are water-soluble hormones that are comprised of amino acids linked via peptide bonds. They are mainly responsible for the regulation of growth and development. An example of a peptide hormone is **insulin** which is made up of 51 amino acid residues. This hormone regulates the metabolism of fats and carbohydrates by promoting absorption of glucose. **Steroid hormones** are lipid-soluble hormones derived from cholesterol. They help control salt and water balance, metabolism, immune functions, and inflammation. **Cortisol** is an example of a steroid hormone which controls some of the body\'s metabolism including the deposition of glucose in the liver. **Amino acid derivatives** are hormones derived from the amino acids tyrosine and tryptophan. They function as promoters of metabolism and immunity. One example is a thyroid hormone known as **epinephrine** or **adrenaline**. This hormone plays a role in the fight-or-flight response by increasing blood flow to muscles. **Fatty acid derivatives** are hormones derived from polyunsaturated fatty acids. They are also called *eicosanoids*. They are mainly responsible for regulating blood pressure and blood clotting. **Prostaglandin** is an example of a fatty acid derivative that is responsible for uterine contractions. **Endocrine glands** secrete hormones directly into the bloodstream. Below are some examples of hormones secreted by specific glands. C:\\Users\\ACER\\Desktop\\SHS11-12\\1.Earth and Life Science\\2nd Quarter Earth & Life\\SCI (Earth and Life Science) Hormones.png **Key Points** - **Hormones** are organic substances released by glands in the endocrine system directly into the bloodstream. They are capable of changing the physiological and metabolic behavior of their target cells to maintain homeostasis. - **Endocrine glands** secrete hormones directly into the bloodstream. These glands work with other organs to maintain homeostasis and regulate most of the body's processes. **The Nervous System: The Control System of the Body** **What makes up the nervous system? How does it work?** The **nervous system** is composed of the **brain**, the **spinal cord**, and the **neurons**. It is considered as the body's storage center and control system. It is mainly responsible for controlling and coordinating all the organ systems by sending messages from the brain through nerve signals. It makes sure that all the parts of the body are working together efficiently. The nervous system is divided into two major parts: the **Central Nervous System** and the **Peripheral Nervous System**.  **Central Nervous System** The **Central Nervous System** (CNS) is composed of the brain and the spinal cord. C:\\Users\\ACER\\Desktop\\SHS11-12\\1.Earth and Life Science\\2nd Quarter Earth & Life\\SCI (Earth and Life Sci) Brain.png\ The **brain** lies within the skull and shaped like a mushroom. It is subdivided into four parts: brain stem, cerebrum, cerebellum, and diencephalon. - The **brain stem** consist of the **medulla oblongata**, **pons**, and the **mesencephalon** continuing down to the spinal cord. It coordinates motor signals from the brain to the body and controls life supporting autonomic functions of the peripheral system. This is also where the facial nerves, which controls your facial expressions, is located. - The **cerebrum** is the bulk of the brain responsible for administering intelligence, emotion learning, and critical judgement. It is divided into two cerebral hemispheres. Each hemisphere controls the body's activities opposite that hemisphere. - The **cerebellum** is the second largest part of the brain responsible for fine-tuning the body and limb movements. - The **diencephalon** is also known as the **forebrain**. It includes the thalamus and hypothalamus. - **Thalamus** is responsible for receiving information from the sensory organs and deliver them to cerebrum for other processes. - **Hypothalamus** is the site of hunger, thirst, anger, and internal body temperature. The **spinal cord** is a long, thin mass of bundled neurons. It serves as a bridge between the central nervous system and the peripheral nervous system. It is responsible for delivering messages from the CNS to PNS and vice-versa. ### Peripheral Nervous System The **Peripheral Nervous System** (PNS) is mainly composed of neurons. **Neurons**, also known as **nerve cells**, are the basic units of the nervous system that communicate within the body by sending electrochemical signals. Their tree-like structures called **dendrites** extend from the cell body to pick up stimuli from the environment, and the long transmitting processes called **axons** extend from the body cell to send signals to other neurons. **Nerves** are bundles of axons that act as information highways that carry signals between the brain and the spinal cord and the rest of the body. PNS can be classified into two groups: the Somatic Nervous System and Autonomic Nervous system. **Somatic Nervous System** (SNS) is responsible for the voluntary movement of the muscles and organs and the reflex movement. On the other hand, **Autonomic Nervous System** (ANS) is responsible for controlling the involuntary movement of the visceral muscle tissue, cardiac muscle tissue, and glandular tissue. It makes your heartbeat and breathing constantly working. The neurons of the ANS is classified into sympathetic neurons and parasympathetic neurons. - **Sympathetic neurons** initiate the "fight or flight" response of the body to stress, danger, excitement, and other emotions. It increases respiration and heart rate, releases adrenaline and other stress hormones, and decreases digestion. - **Parasympathetic neurons** initiate the "rest and digest" response to rest, relaxation, and feeding. It decreases respiration, increase digestion, and allows elimination of wastes. **Key Points** - The **nervous system** is composed of the **brain**, **spinal cord**, and **neurons**. - **Neurons**, also known as **nerve cells**, are the basic and functional units of the nervous system that communicate within the body by sending electrochemical signals. - The **brain** lies within the skull and shaped like a mushroom. - The **spinal cord** serves as a bridge between the central nervous system and the peripheral nervous system. - The nervous system is divided into two major parts: the Central Nervous System and Peripheral Nervous System. - The **Central Nervous System** (CNS) is composed of the brain and spinal cord while **Peripheral Nervous System** (PNS) is composed of nerves cells outside the CNS. - PNS can be classified into two groups: the Somatic Nervous System and Autonomic Nervous system. - **Somatic Nervous System** (SNS) is responsible for the voluntary movement of the muscles and organs and the reflex movement. - **Autonomic Nervous System** (ANS) is responsible for controlling the involuntary movement of the visceral muscle tissue, cardiac muscle tissue, and glandular tissue. - ANS is sub-classified into sympathetic neurons and parasympathetic neurons. - **Sympathetic neurons** initiate the "fight or flight" response of the body to stress, danger, excitement, and other emotions. - **Parasympathetic neurons** initiate the "rest and digest" response to rest, relaxation, and feeding. **Body Systems: How They Work Together** **How do the body systems work together?** **Organ Systems and Their Main Functions** **Organ systems** are the most complex organizations in the human body. Each system has its specific function, but it works with the other organ systems to ensure the organism\'s survival. The 11 organ systems of the body are the respiratory, circulatory, skeletal, muscular, digestive, reproductive, integumentary, lymphatic, excretory, endocrine, and nervous. - The **respiratory system** is responsible for supplying the blood with oxygen. - The **circulatory system** distributes O2, hormones, and nutrients to every part of the body. - The **skeletal system** provides the framework and protection of body parts by encasing vital organs with hard bones. - The **muscular system** helps the body move from one position to another. It also helps circulate the blood throughout the body. - The **digestive system** converts food into usable energy in the form of ATP. - The **reproductive system** enables the organism to reproduce to ensure the survival of the species. - The **integumentary system** protects the body from damage, such as abrasion and loss of water. - The **lymphatic system** transports lymph, which contains infection-fighting white blood cells, throughout the body. - The **excretory system** removes wastes and excess, unnecessary materials from the body fluids to maintain internal balance and prevent organ damage. - The **endocrine system** produces hormones that regulate metabolism, growth, and development. - The **nervous system** coordinates voluntary and involuntary actions of the body. Together with the endocrine system, it controls and regulates other organ systems to maintain the equilibrium of the body. ### Relationships of Organ Systems **Processing and Transport of Nutrients** In humans, food is the main source of energy. It enters the body through the digestive system which breaks it down into nutrients. The muscular system helps moving the food to different organs of the digestive system. For example, muscles around the stomach contract and move food to the small intestine. When the food is broken down into nutrients, these nutrients are transported to different organs and tissues through the circulatory system. Nutrients from the small intestine enter the blood vessels and are then transported by the blood throughout the body. **Transport of Oxygen and Carbon Dioxide** Oxygen enters the body through the respiratory system. This system, together with the circulatory system, delivers oxygen to every cell in the body. As you inhale, the oxygen goes directly into the lungs, specifically in the alveoli where there are capillaries that serve as sites of gas exchange. The capillaries connect to larger blood vessels that transport oxygen to the rest of the body. **Removal of Wastes** Food is processed by the digestive system. After nutrients are absorbed through digestion, the excretory system removes waste products in the form of urine and feces. The organs of the excretory system are also parts of other organ systems. For example, skin is part of the integumentary system. It is also part of the excretory system because it removes liquid waste in the form of sweat. Similarly, the lungs are part of the respiratory system. They remove carbon dioxide from the body, so they are also part of the excretory system. **Maintenance of Homeostasis** The nervous system serves as the control center for maintaining homeostasis in the body. Homeostasis is the property of a system in which an internal factor (e.g. body temperature) is regulated to maintain a stable condition despite changes in external conditions. If there are disruptions of the internal factor, the nervous system sends out signals to other systems to correct the disruption. For instance, it sends signals to the endocrine system which secretes hormones to regulate body functions. These hormones are delivered to the target organs through the circulatory system. **Key Points** - Different organ systems work together to maintain survival of the organism. - The 11 organ systems of the body are the respiratory, circulatory, skeletal, muscular, digestive, reproductive, integumentary, lymphatic, excretory, endocrine, and nervous. **Plant Survival, Earth and Life Science** **Aquatic Plants: Structure and Functions** **What are the characteristics of aquatic plants?** **Aquatic plants**, also called **hydrophytes**, grow in water or in soil permanently saturated with water. They are well distributed around the world. They are often found in areas called littoral zone, which is the shallow part of the water where the sunlight could reach the soil. Aquatic plants can serve as food and habitat for organisms living in different bodies of water such as ponds, lakes, and sea. Some of the major factors affecting the number of aquatic plants growing in a specific body of water include water depth, nutrient availability, and type of soil. One of the most important features of aquatic plants that make them adapt to water is the formation of **aerenchyma** -- a parenchyma tissue with large intracellular air spaces. This tissue is used to store oxygen and transport it to other plant tissues. The stored oxygen is also used by leaves for buoyancy. ### Types of Aquatic Plants Aquatic plants can be classified as floating, submerged, or emergent plants.  **Floating plants** are not rooted at the water's bottom, and the leaves and flowers float and move freely on the water's surface. Some of them are rootless. Others have roots with hair-like structures that dangles from the underside of the leaves. They usually grow in areas where there is a little wave in the water. Some of the common examples of floating plants are water lily, water lettuce, and duckweed. In the tropical areas with heated still waters, floating plants can completely cover the surface within several months. Hence, they are also called aquatic weeds. Duckweeds, for example, can double the surface coverage approximately every two days. **Submerged plants** are aquatic plants which are rooted on the water's bottom but do not extend all the way to the surface. The leaves, stems, and roots grow entirely underwater although some of its leaves float. In addition, they have flowers usually raised above the water surface. They usually grow near the shore up to the deepest part of the littoral zone. They can tolerate fluctuating water levels, shoreline waves, and erosion. Some common examples of submerged plants are pondweed, hornwort, and rice-field water-nymph. Some species of submerged plants are known to have antipollution mechanisms. They are often used for **phytoremediation** -- the use of plants to remove, degrade, and contain contaminants such as heavy metals. **Emergent plants** are rooted on the water's bottom and extend their leaves and stem to the surface. The leaves of these plants have spongy tissues and packed with air spaces. They typically grow along the shore where the water is low, usually less than four feet deep. Some common examples of emergent plants are wild rice, cattails, and pickerelweed. A few species of emergent plants grow via stolons or rhizomes. **Stolons**, also called runners, are stems that allow the plants to spread and reproduce. These stems enable emergent plants to overcrowd other species and allow them to endure periods of environmental stress. On the other hand, **rhizomes** are modified stems, where the shoots and roots arise through the nodes. The shoots and roots serve as the overwintering buds of the plants during cold weather. Example **Seagrasses** are flowering aquatic plants which sometimes found in bays and lagoons. These aquatic plants are so important because they provide food for commercial and recreational fishes. They also add oxygen to the environment and fix sediments to generate materials for the small invertebrates living in the same area. **Key Points** - **Aquatic plants**, also called **hydrophytes**, grow in water or in soil permanently saturated with water. - **Littoral zone** is the area where most aquatic plants are found. - Aquatic plants can be classified as floating, submerged, or emergent plants. - **Floating plants** are not rooted at the water's bottom and the leaves and flowers float and free to move on the water's surface. - **Submerged plants** are aquatic plants which are rooted on the water's bottom but do not extend all the way to the surface. - **Emergent plants** are rooted on the water's bottom and extend their leaves and stem to the surface. - The most important feature of aquatic plants that make them adapt to water is the formation of **aerenchyma**-- a parenchyma tissue with large intracellular air spaces. **Terrestrial Plants: Structures and Functions** **What are the characteristics of terrestrial plants?** **Terrestrial plants** are plants that grow on land. Some of these plants evolved from aquatic environment and developed some structures or parts to survive the terrestrial environment. The parts of terrestrial plants can be divided into the root system and the shoot system. The **root system** consists of roots that obtain nutrients from the soil and store food. On the other hand, the **shoot system** is made up of stems and leaves that carry substances up and down the plant. **The Root System