Biological Systems - Human Biology Notes

**BIOLOGICAL SYSTEMS** **(1) Biological System** **A. Vital Organs** There are five organs considered vital for survival. If one of them stops functioning, the death of the organism is inevitable without medical intervention. 1. **Heart:** Located in the centre of the chest. Keeps blood flowing...

**BIOLOGICAL SYSTEMS** **(1) Biological System** **A. Vital Organs** There are five organs considered vital for survival. If one of them stops functioning, the death of the organism is inevitable without medical intervention. 1. **Heart:** Located in the centre of the chest. Keeps blood flowing through the body. Blood carries substances to cells that they need and also carries away wastes from cells. 2. **Brain:** Focated in the head. Functions as the body's control centre. It is the seat of all thoughts, memories, perceptions, and feelings 3. **The two kidneys:** Located in the back of the abdomen on either side of the body. Filter blood and form urine, which is excreted from the body. 4. **The liver:** Located on the right side of the abdomen. Filtering blood, secreting bile that is needed for digestion, and producing proteins necessary for blood clotting. 5. **The two lungs**: Located on either side of the upper chest. Their main function is exchanging oxygen and carbon dioxide with the blood. **A. Digestive system** **The digestive system** holds all the chemical and mechanical breakdown of food (from complex to monomers) allowing for all monomers to be taken in by cells for respiration. - Digestion: Mechanical (action of teeth) and chemical (low pH and enzymes) breakdown of the food that makes all monomers available for absorption. - Absorption: Uptake of monomers by the epithelial cells along the small intestine, allowing these to reach the circulatory system/cell (cell respiration). - Villi and microvilli in the small intestine serve to increase surface area, absorb nutrients from digested food through specialized cells, secrete mucus to protect the intestinal lining, and enhance the efficiency of digestion and absorption. **B. Circulatory System** **The Circulatory System** is a closed system of blood vessels with a pump (the heart) and valves to make sure the blood flows one way. Vessels: - Veins: Vessels that collect blood at **LOW PRESSURE** from tissues of the body and return it to the atria of the heart. - Thin walls due to low internal pressure. - Carry deoxygenated blood (no O2). - Artities: Vessels that carry blood away from the heart to all tissues/cells in need, at **HIGH PRESSURE.** - Thick and elastic walls to allow/hold all pressure changes. - Carry oxygenated blood (O2 present). - Capillaries: Narrowest blood vessels with a diameter of "1-cell thick". - Highly permeable = + membrane transport. - 1 cell thick maximizes SA:V ratio making the diffusion of CO2/O2 more efficient.  **Blood vessels:** -Arteries -\> carry blood away from the heart, and have thicker walls to deal with high pressure. -Veins -\>  carry blood into the heart, they have a difficult job since they bring blood against gravity towards the heart, therefore they have valves. -Capillaries -\> exchange of substances (oxygen, glucose, nutrients) **Blood:** fluid made of plasma and blood cells 1. WBC (immune system, phagocytes) 2. RBC (O2 transport) 3. Platelets -\> blood clotting -Transports nutrients, gases and waste products **Heart:** - Left side: O2-rich blood - Right side: O2-poor blood - Blood enters the heart through the atria via veins into the upper chambers - ATRIA. - Flows down to the ventricles which pump the blood away from the heart via the arteries. **Blood Circulation in the heart: RA -\> RV-\> Lungs -\> LA -\> LV -\> Body -\> RA** - On the right side: only oxygen-poor blood circulates - Gas exchange happens in the lungs and becomes O2-rich. - Oxygen diffuses from the alveoli to the capillary, and carbon dioxide diffuses from the capillary to the alveoli, so the blood becomes oxygen-rich. - Gas exchange happens in the Body and becomes O2-poor. A diagram of a gaseous process AI-generated content may be incorrect. **C. Respiratory System** 1\. Ventilation - Ventilation is the physical act of taking in/out air into/out of the lungs. - The lungs do **NOT** contain muscle tissue, they cannot "expand & contract" to let air in & out. Instead, they rely on antagonistic muscle pairs -- muscle pairs that work hand-in-hand in opposite directions (one contracts, the other relaxes, and vice-versa). **Antagonistic Pairs** **Inhale** **Exhale** ------------------------------- ------------ ------------ Exterior costal muscles (ECM) Contracts Relaxes Interior costal muscles (ICM) Relaxes Contracts Abdominal muscles Relaxes Contracts Diaphragm Contracts Relaxes Ventilation: The physical act of inhaling/exhaling air (O2/CO2) Gas exchange: The transfer of O2/CO2 between capillaries & alveoli by diffusion Cell respiration: The mitochondria take O2 (and glucose) to produce energy, having CO2 as a waste product. **[ventilation; gas exchange; and respiration.]** Ventilation refers to the process of moving air in and out of the lungs, involving inhalation and exhalation. Gas exchange is the exchange of gases, particularly oxygen and carbon dioxide, between the lungs and the blood, and between the blood and body tissues. Respiration encompasses both ventilation and gas exchange, as well as cellular respiration, which is the process by which cells generate energy (ATP) by oxidizing glucose and other organic molecules, using oxygen and producing carbon dioxide as byproducts. **[Outline the process of ventilation at the level of the (human) respiratory system.]** Ventilation in the human respiratory system involves breathing. When you inhale, your diaphragm and chest muscles contract, expanding your chest cavity and creating space for your lungs to expand. This expansion lowers the air pressure inside your lungs, causing air to rush in through your nose or mouth, down your windpipe, and into your lungs. When you exhale, your diaphragm and chest muscles relax, reducing the space in your chest cavity and causing your lungs to deflate. This increases the air pressure inside your lungs, forcing air out of your lungs and back out through your nose or mouth. **[Explain the process of gas exchange at the level of the (human) respiratory system.]** Gas exchange in the human respiratory system occurs as oxygen from inhaled air diffuses across the thin walls of the alveoli into the bloodstream while carbon dioxide, a waste product, diffuses from the bloodstream into the alveoli, facilitated by the proximity of capillaries and alveoli in the lungs. **D. Nervous System** **Reflex:** An action performed without conscious thought (involuntary), in response to a particular stimulus. **Reflex arc:** Neural pathway that controls a reflex action -\> No brain, just spinal cord & muscle memory.  **Reflex art in steps:** 1. A stimulus is detected by a receptor at the level of the affector nerve. 2. The message is sent through the affector pathway via sensory neurons. 3. The message reaches the spinal cord and relay neurons pass it to the effector pathway and the brain (for post-processing). 4. The messages reach the effector nerve via motor neurons. 5. The effector contracts (reaction occurs). - **Affector**: Nerve cell that directly activates muscles (via reflex arc). - **Effector**: Organ/muscle that reacts to a stimulus. - **Sensory neuron**: Transmits impulses from a receptor, such as those in the eye or ear, to a more central location in the nervous system, such as the spinal cord or the brain. - **Motor neuron**: Transmits impulses from a central area of the NS to an effector. **Sensory neuron** **Function** -------------------- --------------------------- Thermoreceptor Changes in temperature Photoreceptor Changes in light Chemoreceptor Changes in chemicals Mechanoreceptor Changes to pressure/touch Sonar receptor Changes in sounds A diagram of a nervous system Description automatically generated **E.1. Endocrine System (ES)** Homeostasis requires the cooperation of NS & ES because these two systems interact with ALL cells of the body. NS sends an electrical message to/from the brain from/to tissue (voluntary or involuntary), allowing for an action to START/STOP, faster or slower. The endocrine system releases hormones to the blood from specific glands, allowing these to reach targetted cells (Lock & Key theory), ENHANCING/LIMINING a specific action. - Hormones are proteins that only act on targetted cells to allow for a specific action or reaction from cells/tissues. - All secreting glands that make up the ES are: - [Hypothalamus]: controls basic needs -\> Tº, sleeping, eating, blood pressure. - [Pineal] gland: controls your sleeping/waking up time (melatonin). - [Thyroid]: controls intake/output of minerals -\> Ca2+ needed for muscular contraction. - [Adrenal gland]: controls metabolism (fight, flight & freeze) (adrenaline). - [Pancreas]: controls our appetite & blood sugar levels (insulin/glucagon). - [Ovaries & Testies]: control primary & secondary reproductive characteristics. **Hormone** **Neuron** ------------------------------ -------------------- ------------------- **Type of message** Chemical Nerve impulses **Where is it transported?** Blood Neuron network **Speed of transportation** Longer Faster **Destination** All targeted cells Only muscle cells **Length of response** Long Short **Insulin**: hormone secreted by the pancreas as a response to high levels of glucose in the blood, cells take in glucose, sugar blood levels fall -\> loss of appetite. **Glucagon**: hormone secreted by the pancreas as a response to low levels of glucose in the blood, cells stop taking in glucose, sugar blood levels rise -\> gain appetite. Insulin and glucagon work in a negative feedback loop:  **E.2. Tropism** -Plants respond to stimulus by changing their rate of direction of growth. They may grow either away or towards a stimulus. - Stimulus is a change in the organism\'s environment that can be detected by its sense organs. - Positive growth = towards stimulus. - Negative growth = away from the stimulus. -These responses are called tropisms: A tropism is a growth response by a plant, in which the direction of the growth is affected by the direction of the stimulus. - **[Phototropism]** = stimulus is light (shoots grow towards the light). - **[Gravitropism]** = stimulus is gravity (shoots grow against the gravity & roots grow towards it). -Both the most extreme and -tip- of the shoots and roots have a receptor (at the level of the cell membrane); act "like" a sensory neuron). If this receptor is stimulated, it releases a hormone called **[auxin]**. - **[Hormone]**: chemical substance (messenger) that targets a cell (or tissue) activating or de-activating an action/pathway of actions. - **[Auxin]**: Is a plant hormone responsible for cell elongation. A diagram of a cell structure AI-generated content may be incorrect. **F. Immune System** **The immune system** is responsible for recognizing, responding and eliminating any invader (anything that does not share the host\'s DNA). Invaders can be: 1. Pathogen: A living thing that causes/starts a disease. 2. Allergen: A living/non-living thing that causes an allergic reaction. **Immune system:** 1-Innate immune -\> non-specific (just there). 2-Adaptive/True immune -\> specific (active response). **Innate Immune System** -- First line of defence 1. **Natural Barriers:** Act like barriers to stop pathogens from entering tissues and the blood system. a. Physical -- eyelashes/hair/skin. b. Chemical -- wax, snot/boogers, tears, saliva -\> mucus membranes 2. **Macrophages (in your blood):** White blood cells that roam the blood with the function of detecting "Self vs. Non-Self" of all the things roaming inside of us. c. Reads intruders DNA -\> Self vs. Non-Self? d. Non-Self? -\> Engulfs (eats & digests) invader. **Adaptive Immune System** -- Second line of defence Assuming that the macrophages fail; Before they die out, they send an SOS to the body. 3. **T-Cells:** detect SOS of macrophages and: e. It roams the body and kills any infected cells. f. Activates B-Cells 4. **B-Cells:** are activated and they will make copies of themselves. Copies will transform into: g. [Plasma Cells] -- Produce antibodies to isolate & destroy invaders. h. [Memory Cells] -- Are to roam the body for better recognition of the same invader in the future  **[Antigen:]** Is a membrane protein on the outside of pathogens that the immune system can recognize -- Self vs. Non-Self? **[Antibodies:]** These are Y-Shaped proteins that attach to specific pathogens by having an "antigen specificity". -\> They stick to pathogens: Lock & Key Theory A screenshot of a cell phone AI-generated content may be incorrect. 1. Cluster 2. Isolation **DNA and Heritage** \(1) Genome -- Chromosomes and Genes **A. DNA:** Molecule that contains genetic code that determines the shape and structure of living things. **B. Chromosomes:** DNA is divided into several chromosomes. They are small bodies in the nucleus of a cell that carry the chemical "instructions" for the reproduction of the cell. 1. **Diploid cell:** A cell that has a nucleus containing two sets of each chromosome. 2. **Haploid cell:** A cell that contains only a single set of unpaired chromosomes. **(2) Genes and Alleles** Each chromosome contains lengths of genetic code that determine different characteristics -- these lengths of code are called genes. A gene is the unit of inheritance, passed down from one generation to the next. In other words, a gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. Every gene occupies a specific position on a chromosome. And even though the total number of genes is not yet known precisely for humans or other species, there are estimates which show some trends: ▪ Bacteria have fewer genes than eukaryotes. ▪ Some other animals have fewer genes than humans, but some have more. ▪ Plants may seem less complex than humans, but some have more genes. There are different versions of some genes that have almost the same base sequence but differ in just one or a very small number of bases. These variant forms are called alleles.  **(3) Genome** The genome is the whole of the genetic information of an organism. The size of a genome is therefore the total amount of DNA in one set of chromosomes in that species. It can be measured in millions of base pairs (bp) of DNA. Sizes of genomes vary. Examples: **(3) Cell Cycle** The zygote, the first cell we have, needs to make copies of itself so that there are enough cells to make the whole organism. But the whole organism will also need to make copies to (1) grow in size, (2) replenish lost cells due to trauma, and/or (3) regenerate cells. Every time a cell needs to make a copy, i.e: to reproduce itself, it needs to undergo the CELL CYCLE. G1 - Growth Phase \#1: The cell grows in size to prepare for DNA replication. The cell needs to make sure that the doubling of all its chromosome content will fit. The cell is diploid, 2n S-Phase, interphase: The cell undergoes DNA replication doubling its chromosome content. The cell becomes tetraploid, 4n. G2 -- Growth Phase \#2: The cell duplicates each organelle at least once. The cell needs to ensure that all its organelles are at least doubled before cytokinesis so that the daughter cells are fully functional. Cell is still a tetraploid, 4n. Mitosis: The process of cell duplication/reproduction, during which one cell gives rise to 2 genetically identical daughter cells (4n 2n & 2n). Stages of Mitosis: - Only happens in sex organs testicles & ovaries. - 2n n & n two haploid cells **Meiosis:** Meiosis is the process that halves chromosome numbers to create sex cells - sperm and egg cells - also called gametes. Sex cells are formed in the gonads (ovaries and testes). While all the egg cells formed will always carry an X chromosome. Half of the produced sperm cells will carry an X chromosome and the other half a Y chromosome. In meiosis, a diploid nucleus divides twice to produce four haploid cells. The DNA of the chromosome is replicated before the first division, so each chromosome consists of two sister chromatids, but the DNA is not replicated between the first and second divisions. It is the separation of pairs of homologous chromosomes in the first division of meiosis that halves the chromosome number. In summary: 2n → DNA replication: 4n → Cell cycle: 2x 2n → Meiosis, 4x n. At the end of the process, the haploid cells produced are not identical -- meiosis results in genetic variation. This means that whichever sperm cell and/or egg cell are produced, both the maternal and paternal chromosomes always contain new combinations of genetic material. Cellular Reproduction: Process by which cells duplicate their contents and then divide to yield multiple cells with similar, if not duplicate, content. - Sexual reproduction -- a mode of reproduction involving the fusion of haploid gametes (egg + sperm). Meiosis. - Asexual reproduction -- a mode of reproduction in which offspring comes from a single-parent organism (clone). Mitosis.  **(4.A) Manufacturing of Proteins** Transcription: 1\. DNA helicase opens the double helix. 2\. RNA polymerase makes a copy of DNA. 3\. Once the copy is done (mRNA), the copy leaves the nucleus. Translation: 1\. Ribosome "sits" on the mRNA and reads codon by codon -- i.e.: 3 nucleotides in a go. -Does this along the ER = "highway" 2\. Protein is produced aa by aa In summary, DNA codes for proteins in the following way: 1\. Helicase → DNA in the nucleus unwinds and 'unzips' -- the bases are exposed. 2\. RNA polymerase → Transcription allows for a copy of the genetic code to be taken -- the copy itself is mRNA. 3\. The mRNA travels out of the nucleus into the cytosol, reaching the ribosome. 4\. Ribosome → Translation occurs at the ribosome -- mRNA is read, determining the order of amino acids (building blocks of proteins) **(4.B) Synthesis of Amino Acids** The amino acid sequence of proteins is determined by mRNA according to the genetic code. The genetic code that is translated on the ribosome is a triplet code, this means that three bases code for one single amino acid. A group of three bases is called a codon. If there are 4 bases (A, T, G and C) that can assume 3 positions for each codon, then there are a total of 64 codons (43 ). This gives more than enough codons to code for the 20 amino acids in proteins Amino acids are then linked together by condensation reactions to make proteins or peptides - a short chain of amino acids. The amino acids in a peptide are connected in a sequence by bonds called peptide bonds. ▪ Chains of fewer than 40 amino acids are called peptides. ▪ A dipeptide is a molecule consisting of two amino acids linked together. ▪ A polypeptide consists of many amino acids linked by peptide bonds that form an unbranched (linear chain). ▪ A protein consists either of a single polypeptide or more than one polypeptide linked together. **(5) Mutations** Mutations are random changes to the base sequence of a gene. The change may or may not result in a change to the physical characteristics (or phenotype) of an organism. Mutations that occur in a sex cell (gamete: sperm; or egg) can be passed to the next generation, whereas mutations that occur in the body (somatic) cells may be harmless or may lead to irreversible damage. Although mutations are important as they are a source of the genetic variation (different alleles) that is necessary for evolution to occur, very few mutations prove to be beneficial and some cause genetic diseases or cancer  **(6) Inheritance** A paper with writing on it AI-generated content may be incorrect.  A screenshot of a computer AI-generated content may be incorrect. A screenshot of a test AI-generated content may be incorrect. **(7) Pedigree Diagrams** A pedigree diagram is a geneological tree that tracks down a trait over generations. - Autosomal recessive trait/disease The trait/disease is recessive on any chromosome that is not a sex chromosome. - A disease can be autosomal recessive when it is manifested by the presence of two recessive alleles; or autosomal dominant, when it is manifested by the presence of two dominant alleles. A carrier is an individual that does not have the disease but has the allele of it present in its gene (heterozygous).  **Metabolism & Bioenergetics** **Photosynthesis** **State the [balanced] chemical formula of photosynthesis.** A black arrow pointing to sunlight AI-generated content may be incorrect. **Explain photosynthesis by including its (1) complete chemical reaction, (2) source of substrates (xylem vessels -- transportation), and (3) destination of products (phloem vessels -- translocation).** - **Complete Chemical Reaction:** In the presence of sunlight, plants convert carbon dioxide (CO2​) and water (H2O) into glucose (C6H12O6​) and oxygen (O2​). - **Source of Substrates:** Water is transported from the roots to the leaves via **xylem vessels**, while carbon dioxide enters the leaves through **stomata**. - **Destination of Products:** The glucose produced is transported from the leaves to other parts of the plant through **phloem vessels** (a process called **translocation**), while oxygen is released into the atmosphere via stomata. **Identify the main limiting factors of photosynthesis -- i.e., light, CO~2~ and temperature and describe how they affect the rate of photosynthesis.** **Precisas mas nao sei qual** - Light Intensity: Affects the rate of photosynthesis as more light provides more energy for the reaction. Low light reduces the rate. - CO₂ Concentration: Photosynthesis rate increases as CO₂ levels rise until the saturation point, where it plateaus. - Temperature: Enzyme activity increases with temperature until an optimal point, after which enzymes denature, causing a drop in the photosynthetic rate. **Identify indicators of photosynthesis (oxygen production, carbon dioxide uptake and increase in biomass).** **Nao me lembro** - Oxygen Production: Measuring oxygen release is an indicator of the photosynthesis rate. - Carbon Dioxide Uptake: A reduction in CO₂ levels in the surrounding environment indicates photosynthesis. - Increase in Biomass: Plant growth and the accumulation of glucose are signs of active photosynthesis. - Height growth. **Transport in plants** **Recognize and label parts of a plant leaf.**  A diagram of a plant cell Description automatically generated **Outline how water travels from the soil to the leaves in plants (xylem);** Xylem tissue transports water and minerals up the stem from the roots to the shoots and leaves. This transport occurs in one direction only (upwards). **Outline how organic compounds (food) travel from the soil to the leaves in plants (phloem);** Phloem tissue transports sugars produced in the leaves up and down the stem to growing and storage tissues. **What is transpiration?**  **Explain how different environmental conditions affect the rate of transpiration** A screenshot of a cell phone Description automatically generated **Respiration** **Outline why glucose is the main source of energy for most organisms, such as human beings.** Glucose is the primary energy source because it is easily broken down to release ATP (adenosine triphosphate) during cellular respiration, which fuels cellular activities. Because it is soluble and easily transported from blood to cells. It is also easy to digest compared to lipids and proteins. **What is cellular respiration?** Cellular respiration is the body\'s process of releasing energy from digested food (organic compounds such as glucose). The energy is released in a controlled way (this means by chemical reactions catalysed by enzymes). The type of cellular respiration is called aerobic respiration because energy is released in the presence of oxygen. **Distinguish between anaerobic respiration and aerobic respiration** Anaerobic occurs in the absence of oxygen, examples of anaerobic respiration: Lactic acid fermentation: used to produce yoghurt. - Glucose Lactic acid + little energy (2 ATP) - Occurs in some bacteria and, muscle cells. Alcoholic fermentation: used to produce wine/bear/bread and bioethanol. - Glucose ethanol + CO2 + little energy - Occurs in yeast cells and plant cells **Explain how/why the human body has the capacity to shift from aerobic to anaerobic respiration at the muscular cellular level.** When oxygen is insufficient during intense exercise, muscle cells switch to anaerobic respiration, producing ATP without oxygen but resulting in lactic acid buildup, which causes muscle fatigue. **Summarize the 'destinations' of glucose within the human body -- cellular level.** - Immediate Energy: Glucose is used in cellular respiration to generate ATP. - Storage: Excess glucose is stored as glycogen in the liver and muscles or converted to fat. **Compare and contrast aerobic and anaerobic respiration in terms of (1) substrate/s, (2) location of chemical reaction/s, and (3) net ATP.**  A diagram of a diagram of oxygen Description automatically generated with medium confidence  **Metabolism** **Explain the concept of metabolism, including anabolism and catabolism in terms of (1) energetic flow (store/release), (2) action on tissue (build/destroy), and (3) reaction type (condensation/hydrolysis).** A close up of words Description automatically generated  A diagram of different types of catabolism Description automatically generated **Outline the role of catalysts (enzymes) in metabolic reactions.** Enzymes act as catalysts, speeding up metabolic reactions without being consumed, by lowering the activation energy needed for reactions to occur.  **Recognize the concepts of photosynthesis and respiration as metabolic processes.** - Photosynthesis is anabolic (builds glucose). - Respiration is catabolic (breaks down glucose). **Describe and sketch the four steps of the Lock and Key Theory.** - Step 1: The enzyme has a specific active site. - Step 2: The substrate fits into the enzyme\'s active site (like a key fits into a lock). - Step 3: The enzyme catalyzes the reaction, transforming the substrate. - Step 4: The product is released, and the enzyme remains unchanged. - A diagram of a complex Description automatically generated **Bioenergetics** **Sketch and outline the ATP cycle.**  **Ecosystems and Human Impact** **Ecology concepts** **Define the different ecology levels: Species, Populations, Communities, Ecosystems and Biomes** **Species** **A group of organisms that can interbreed and produce fertile offspring.** ----------------- ------------------------------------------------------------------------------------------------------- **Populations** **A group of individuals of the same species living in a specific area.** **Communities** **Different populations of organisms interact in the same environment.** **Ecosystems** **A community of organisms and their physical environment interact together.** **Biomes** **A large geographic area with similar climate, vegetation, and organisms (e.g., deserts, forests).** **Define** habitat and niche. **Habitat: The physical environment where an organism lives (e.g., a pond for a frog).** **Niche: The role an organism plays in its ecosystem, including its diet, interactions, and environmental conditions it needs to survive** **Distinguish and explain** between different types of species interactions **-** symbiotic (mutualism, parasitism, and commensalism), intra- and inter-competition, predator-prey, etc. **[Symbiotic Relationships]** - **Mutualism (+/+)**: Both species benefit (e.g., bees and flowers). - **Parasitism (+/-)**: One species benefits while another is harmed (e.g., ticks on dogs). - **Commensalism (+/0)**: One species benefits, while the other is unaffected (e.g., barnacles on whales). **[Competition]** - **Intraspecific**: Competition within the same species (e.g., two lions fighting for territory). - **Interspecific**: Competition between species (e.g., lions and hyenas competing for prey). **[Predator-Prey Relationship]** - Predators hunt and consume prey (e.g., foxes hunting rabbits). **Discuss** the cycle of predators and prey. **[Predator-Prey Cycle]:** Predator and prey populations are interlinked: - If prey populations increase, predator numbers rise. - As predators consume more prey, the prey population declines, leading to a decline in predators. - When predators decrease, prey populations recover, repeating the cycle. - A food chain shows energy transfer through an ecosystem:\ **Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Apex Predators** - Each level is a **trophic level** representing energy flow. **Distinguish** the nutrition mode of organisms (autotrophs versus heterotrophs) and link it to the roles of producers, consumers and decomposers. **Autotrophs (Producers):** Make their food (e.g., plants via photosynthesis). **Heterotrophs (Consumers):** Depend on others for food. - Primary consumers (herbivores) - Secondary consumers (carnivores/omnivores) - Tertiary consumers (top predators) **Decomposers:** Break down dead matter, recycling nutrients (e.g., fungi, bacteria). **Explain** why decomposers are essential for the cycling of nutrients and maintenance of energy flow within ecosystems. Decomposers break down dead plants and animals, returning important nutrients to the soil. This helps plants grow, keeping the food chain going. They also prevent waste from piling up and release energy back into the ecosystem. Without decomposers, nutrients would be trapped in dead matter, and life would struggle to continue. **Design** food chains. Food Chain Images - Free Download on Freepik **Explain and design** food webs. **Identify** the trophic levels in food webs and food chains **Design** an energy pyramid -- include (1) trophic levels, (2) the nutrition mode of organisms, and (3) net energy within the level. **Outline** the energetic losses in food chains **and link** them to population numbers within each trophic level.  **Define** keystone species A **keystone species** is an organism that has a much bigger effect on its ecosystem than other species. Even if it is not the most common, it plays a key role in keeping the ecosystem balanced. **Describe** the role of a keystone species within an ecosystem. Keystone species help maintain ecosystems in different ways: 1️. **Controlling Populations** -- They keep other species from overpopulating, which helps maintain balance. - Example: Wolves in Yellowstone prevent deer from overgrazing, which protects plants and trees. 2️. **Supporting Biodiversity** -- By keeping ecosystems stable, they allow many different species to survive. - Example: Sea otters eat sea urchins, stopping them from destroying kelp forests that shelter many animals. 3\. **Shaping Habitats** -- Some keystone species change their environment in ways that help other species survive. **Why Are Keystone Species Important?** - If a keystone species disappears, the entire ecosystem can fall apart or change drastically. - They help keep food chains stable by maintaining natural balance. - Protecting keystone species is important for keeping ecosystems healthy. **Cycles of matter in ecosystems** **Explain **the importance of the carbon cycle [and] the nitrogen cycle in maintaining the flow of energy and matter cycle within all ecosystems on Earth. **Carbon Cycle:** - **Role**: Transfers carbon through the atmosphere, organisms, water, and soil. - **Energy Flow**: - **Photosynthesis**: Plants convert CO₂ into glucose (energy). - **Respiration**: Organisms release CO₂ back into the atmosphere. - **Importance**: Essential for building organic molecules and regulating climate. **Nitrogen Cycle:** - **Role**: Recycles nitrogen for proteins and DNA. - **Key Processes**: - **Nitrogen Fixation**: Bacteria convert atmospheric N₂ into usable forms for plants. - **Decomposition**: Returns nitrogen to the soil after organisms die. - **Importance**: Ensures nitrogen availability for growth and ecosystem health. **Sketch and label** the carbon cycle [and] the nitrogen cycle. **Human impact** **Analyse** human population growth over the past 10,000 years. **Analyse, evaluate and discuss** main human activities that impact the environment -- A HIPPO (agriculture, habitat loss, invasive species, pollution, human population, and overharvesting). **Process and evaluate** information about a case study (Industrial Revolution and the peppered moths) to **explain** the human influences on population numbers and biodiversity