Topic 1: Characteristics of Living Things PDF

# Topic 1: Characteristics of Living Things ## The difference between a living and a non-living thing An organism or living things are beings that show characteristics of life. These are called the seven vital functions. If we observe these organisms and the processes which take place inside them,...

# Topic 1: Characteristics of Living Things ## The difference between a living and a non-living thing An organism or living things are beings that show characteristics of life. These are called the seven vital functions. If we observe these organisms and the processes which take place inside them, we can find all these 7 vital functions. Living things do the following vital functions: 1. Nutrition 2. Respiration 3. Excretion 4. Growth 5. Movement 6. Sensitivity 7. Reproduction For an organism to be alive it must show all of them. Each of the seven is important for a species to live efficiently and survive to the next generation! ## 1. Nutrition All living organisms need food. Food is important for energy, growth and repair (replace worn out tissues). There are mainly two ways for organisms to obtain their food; these are autotrophic nutrition and heterotrophic nutrition. | Producer | Primary Consumer | Secondary Consumer | |---|---|---| | Cabbage | Caterpillar | Robin | | Autotrophic | Heterotrophic | Heterotrophic | ## Autotrophic Nutrition Autotrophic organisms or autotrophs such as plants and algae (and some bacteria) which produce their own food (organic substances) by photosynthesis thus are called producers because they produce their own food. Autotrophs rake in simple inorganic substances which are carbon dioxide and water and build them up into complex organic substances such as glucose. To do this the autotroph needs the energy from sunlight, which is captured using the green pigment in the leaf cells called chlorophyll. This process is called photosynthesis. **Photosynthesis Word Equation:** Light Energy Water + Carbon dioxide → Glucose + Oxygen Chlorophyll **Photosynthesis Chemical Equation:** Light Energy $6H_2O + 6CO_2$ → $C_6H_{12}O_6 + 6O_2$ Chlorophyll ### Examples of Autotrophs * Plants * Algae * Photosynthetic bacteria ## Heterotrophic Nutrition Organisms that have to feed on ready-made organic compounds (food) are called heterotrophs. (These ready-made organic compounds are produced by plants; hence the food chain). ### Examples of Heterotrophic nutrition | | | | |---|---|---| | Rabbit - Herbivore | Lion - Carnivore | Bear - Omnivore | | Eats only plant material. | Eats only other animals. | Eat both animals and plants. | | Tapeworm - Endoparasite | Flea- Ectoparasite | Mould - Decomposer | | Feeds on the inside of a host. | Feeds on the outside of a host. | Breaks down dead or decaying matter. | ## 2. Respiration Living organisms need food because this provides them with energy. Food is stored energy; organisms are able to get this energy from food by respiration. Respiration is the breakdown of glucose (food) into simpler products to release energy in the form of ATP. Glucose is a simple carbohydrate and is found in many types of food. With the energy produced by respiration, an organism can move, repair and grow. Respiration is a chemical reaction which happens in all the cells. There are two types of respirations: Aerobic (needs oxygen) and Anaerobic (without oxygen). ## 3. Excretion The removal of waste products, resulting from metabolism (chemical reaction), from the body. A living organism is like a chemical factory, constantly breaking down substances to produce energy, repair and grow. All these chemical reactions together are referred as the Metabolism. Some of the by-products of metabolism are very poisonous to the organism itself; therefore, they must be removed for its survival. ### Examples of Excretion in living things | | | | |---|---|---| | Gaseous exchange: Removal of Carbon Dioxide. | Sweating | Removal of Urea | | | | | | Gaseous exchange: Removal of Oxygen in autotrophs. | Leaf Shedding | | **Note:** Removal of faeces (pooping) is not an example of excretion. ## 4. Growth Growth is the increase in size, mass or volume of an organism through cell division and enlargement. Food is required for growth to take place. When substances and nutrients are taken into the organism from the outside; they are then built up into the structures of the body. Most living organisms begin their existence as a single cell; this cell then undergoes multiple cell divisions and a multicellular organism forms. Unicellular organisms grow until mature. Growth continues throughout the life of some organisms such as in woody plants; or it may stop at maturity like in humans. Growth is controlled by growth hormones. One must keep in mind that even though growth might have stopped; the organism is constantly replacing worn out tissue and renewing itself. ## 5. Movement Movement is the change in position of any part of an organism's body (even if this is for a short period of time during the life of the organism). When the entire organism (ex. Animals) goes from one place to another it is called locomotion. Plants move parts of their bodies towards the light source and the opening and closing of flowers and leaves. Unicellular organisms may have cilia and/or flagella to move. ## 6. Sensitivity Sensitivity is the ability of a living organism to respond to stimuli or a change in the environment. Organisms respond to stimuli and are aware of the surroundings. When you prick your finger with a needle; you remove your finger immediately. The touch (+pain) of the needle is the stimulus; the removing of the finger is the reaction. Plants respond to stimuli slowly. They react to the direction of light, water and gravity. The main stimuli are: touch, chemicals (taste and smell), pH, heat, light and sound. Structures such as the eye (detect light) are called receptors. Receptors are made up of sensory cells, these cells form a sense organ. ## 7. Reproduction No organism lives forever. Living organisms produce offspring, this ensures the survival of the species. There are two types of reproduction, Sexual and Asexual. ### Sexual Reproduction Sexual reproduction usually involves the union of two individuals, male and female. Male produces sperm and females the eggs. Sperms and eggs are called sex cells, reproductive cells or gametes. When a sperm reaches an egg they unite. This is called Fertilisation. The fertilised egg becomes an embryo which develops into a new individual. Most animals and plants reproduce sexually. In plants, the male gamete is the pollen and the embryo is the seed. ### Asexual Reproduction Involves an organism that can reproduce on its own. For example, it may spit in two. Asexual reproduction may take place very quickly. The offspring are IDENTICAL to the parent. ## Cells Cells are the basic unit of life. The cell is the smallest part of the organism that shows the 7 vital functions. Cells are made up of atoms which form molecules; these molecules form structures and membranes in cells. Some cells called Eukaryotic cells have more complex structures called membrane-bound organelles. An organism made up of one cell is called unicellular. Organisms with more than one cell are called multicellular. Microscopes are needed to see cells. ## Prokaryotic and Eukaryotic cells ### Prokaryotic cells Prokaryotic cells are cells without a nucleus. Their DNA is clumped but it floats around the cell. The cells are surrounded by a pellicle (membrane). Prokaryotes are usually unicellular (1 cell only) and don't have any membrane-bound organelles either (so they don't have vacuoles, mitochondria, chloroplasts and nuclei). ### Eukaryotic Cells Eukaryotic cells are cells with a cell membrane, nucleus and other membrane-bound structures which are called organelles. Eukaryotes may be unicellular or multicellular. Most living things are Eukaryotic: Animals, Plants, Fungi and Protists. ### Basic Eukaryotic cells: #### Animal cell * Cytoplasm * Nucleus * Cell membrane * Mitochondrion ## Organelles in animal and plant cells * **Cytoplasm:** Where all activities in the cell take place. It is a jelly-like substance a thick fluid within the cell membrane mostly made up of water. Cytoplasm stores food in the form of starch grains (in plants) or glycogen granules (in animals). Hundreds of chemical reactions happen in it. * **Suspended in it are organelles; these are membrane-bound structures which carry out one function. Ex. Nucleus, mitochondria and Chloroplasts (in Autotrophs).** * **Cell Membrane:** Semi-permeable outer border of the cells that controls what goes in and out of the cell. Contains the cell material and acts as a barrier to the outside environment. ## Organelles found in Plant Cells The plant cell contains the nucleus, the cell membrane, cytoplasm and the mitochondria, just like the animal cell, but it contains 3 more structures. These 3 structures are the cell wall, vacuole and chloroplast. * **Cell wall:** A fully permeable layer which allows all substances to pass through. Found outside cell membrane and provides support and structure. Mostly made of cellulose (a tough elastic material). This makes the plant cell more rigid. The cell wall gives shape to the cells and prevents them from bursting when a lot of water goes into the cell. * **Vacuole:** Is in the centre of the plant cell, it is membrane-bound structure filled with cell sap. The vacuole stores food and water. Small temporary vacuoles may be found in animal cells but a permanent large central vacuole is found in plant cells. * **Chloroplast:** Organelles in the cytoplasm of plants. They contain a green pigment (colour) called Chlorophyll. These are only found in the green parts of plant (which are exposed to the sun). It is used to trap sunlight energy to produce glucose (food) by photosynthesis. ## Animal vs Plant cells | | | |:---:|:---:| | Animal | Plant | | Cell wall not present | Cell wall present | | Has no Chloroplasts | Has Chloroplasts | | Small temporary vacuoles | Permanent large central vacuole | | Does not photosynthesise | Photosynthesises | | Has a spherical shape | Has a cuboidal shape | | Nucleus at the centre | Nucleus and chloroplasts at the edge | ## Animal Photomicrograph as seen under the Electron Microscope * mitochondria * cell membrane * nucleus * cytoplasm ## Plant Photomicrograph as seen under the Electron Microscope * Vacuole * Mitochondrion * Chloroplast * Cell wall * Cell membrane ## Cell Division New cells are formed by cell division. A cell divides and produces 2 identical daughter cells. Daughter cells may later continue dividing or develop into a distinct shape becoming specialised for a particular function. Specialised cells can't divide. Cell division enables an organism to grow and takes place more in growing regions such as bone ends and root tips. ## Cell specialisation and Organisation These cells vary a lot in shape. In a human body there are many different types of cells, each with a particular function to carry out. In our body, there is division of labour (just like in a factory where each person has his or her job to do. Multicellular organisms are made up of different types of cells. This helps division of labour within an organism. One type of cell serves a certain function while others have a different function. Each cell is specialised to do a particular job. This is known as cell specialisation. 1. A group of specialised cells of similar structure and function form Tissues. 2. A number of tissues working together to do a particular function form organs. 3. Multiple organs working together form an Organ system. 4. Different organ systems working together form the organism. Ex. Specialised muscle cells form muscle tissue. Multiple tissues (ex. Muscle + Epithelium) form the stomach. The stomach together with other organs like the intestines and the esophagus form the digestive system. The whole organism is made up of many systems working together; ex, digestive, nervous, circulatory etc. ## Specialised Cells | Structure | Specialised Cell function | |:---:|:---:| | Red blood cells | Red blood cells carry oxygen or carbon dioxide. It has no nucleus and contains a chemical called haemoglobin which joins with oxygen. | | White blood cells | White blood cells are part of the immune system. They are like little warriors in your blood waiting to attack invaders, like viruses and bacteria. They can produce antibodies to fight off diseases. | | Nerve cells | Nerve cells carry messages to the brain via electrical messages. They are long and have myelin sheath to carry out messages faster. | | Muscle cells | Muscle cells contract and relax to produce movement. They need a lot of energy therefore they have a lot of mitochondria. | | Sperm cells and Egg cells | Sperm cells and Egg cells are the male and female sex cells. Sperm cells are small and have a flagellum to swim to the egg cell. Egg cells are large and round. Both the sperm and egg cell have half the amount of DNA. | | Root hair cells | Root hair cells absorb water from the soil. They have thin outgrowths called root hairs to increase the surface area by which water is absorbed. | | Palisade cells (Leaf Cells) | Palisade cells (Leaf Cells) produce glucose by photosynthesis. They have a lot of chloroplasts to do more photosynthesis. |