United Grade 10 Biology
Chapters: 4
1. From molecules to organisms: structures and processes
DNA codes for proteins · Levels of organization in multicellular organisms · Homeostasis and feedback · Mitosis and differentiation · Photosynthesis · Building carbon-based molecules · Cellular respiration
- Protein Synthesis: From Gene to Protein – A gene is a stretch of DNA that holds the recipe for one protein. In transcription, the cell copies the gene into messenger RNA (mRNA) inside the nucleus; U replaces T. The mRNA goes to a ribosome in the cytoplasm. In translation, the ribosome reads the mRNA three bases at a time (a codon). Each codon matches one amino acid, carried in by a transfer RNA (tRNA). The amino acids join into a chain that folds into a protein. A change in the DNA (a mutation) can change the protein.
- Tissues: Plant and Animal Tissues – A tissue is a group of similar cells that do one job together. Cells form tissues, tissues form organs, organs form organ systems and systems form an organism. Plants have dividing meristematic tissue and non-dividing permanent tissue, including xylem (water up) and phloem (food both ways). Animals have epithelial, connective, muscular and nervous tissue. Bones, muscles and joints need good posture, exercise and food rich in calcium.
- Homeostasis – Homeostasis is how the body keeps its internal environment (blood and tissue fluid) steady even when the outside world changes. It controls body temperature (about 37 °C), blood glucose (about 4–6 mmol/L), water and salt, and blood pH (about 7.4). It mostly uses negative feedback: a receptor senses a change, a control centre decides, and an effector brings the level back to its set point.
- Cell Cycle and Cell Division – A cell grows, copies its DNA and splits in a fixed order called the cell cycle: interphase (G1, S, G2) and M phase. In S phase the DNA doubles (2C → 4C) but the chromosome number stays the same. Mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis give two cells identical to the parent – it is an equational division used for growth and repair. Meiosis has two divisions; in meiosis I homologous chromosomes pair, cross over and separate, halving the chromosome number (2n → n). It makes four haploid cells for gametes and creates variation.
- Life Processes and Photosynthesis – Life processes are the jobs every living body must keep doing to stay alive: nutrition, respiration, transport and excretion. Green plants do nutrition by photosynthesis: using sunlight and chlorophyll, they turn carbon dioxide and water into glucose and give out oxygen.
- Biomolecules – A cell is mostly water, plus four big families of carbon compounds: proteins, carbohydrates, lipids and nucleic acids. Grinding tissue in acid separates small molecules (acid-soluble pool) from big ones – proteins, polysaccharides and nucleic acids (acid-insoluble pool). Proteins are chains of amino acids folded into four levels of structure. Polysaccharides are chains of sugars; lipids are fatty acids on glycerol; nucleic acids are chains of nucleotides. Enzymes are protein catalysts that bind a substrate at the active site, lower the activation energy, and are affected by temperature, pH, substrate level and inhibitors.
- Respiration: Aerobic, Anaerobic and the Human Lungs – Respiration is the breakdown of food, usually glucose, inside cells to release energy, stored as ATP. With oxygen (aerobic) glucose is fully broken into carbon dioxide and water and gives much energy; without oxygen (anaerobic) it gives little energy and makes ethanol (yeast) or lactic acid (muscles). Our lungs bring oxygen to the blood through millions of alveoli.
2. Ecosystems: interactions, energy and dynamics
Carrying capacity · Biodiversity and population factors · Aerobic and anaerobic cycling of matter · Energy pyramids · Photosynthesis and respiration in the carbon cycle · Ecosystem stability and change · Reducing human impact on biodiversity · Group behavior and survival
- Population Ecology: r and K Species, Survivorship and Human Populations – Species follow different life plans. r-selected species have many small young and give no care; K-selected species have few big young and care for them. Survivorship curves show who dies when (Type I late, Type II steady, Type III early). Generalists use many resources; specialists need one. For humans, age pyramids, the total fertility rate (replacement about 2.1) and the four stages of the demographic transition explain how populations grow, level off or shrink.
- Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).
- Diversity and Classification of Living Organisms – Earth has millions of kinds of living things, and India is one of the richest places. To study them, we sort them into groups by asking simple questions about their bodies: Is there a nucleus? One cell or many? Can it make its own food? This gives five kingdoms: Monera, Protista, Fungi, Plantae and Animalia. Animals split into invertebrates and vertebrates. Every species gets a two-part scientific name. Viruses are not cells, so they fit in no kingdom.
- Ecosystems in Depth: Biomes, Nutrient Cycles and Disruption – Biomes are large regions with similar climate and life. On land, temperature and rainfall decide the biome; in water, salt, depth, light and flow decide the zones. Matter cycles through ecosystems: nitrogen moves between air, soil, organisms and back through fixation, nitrification, assimilation, ammonification and denitrification; phosphorus cycles slowly between rock, soil, water, organisms and sediment with no gas stage. Decomposers recycle matter with oxygen (aerobic) or without it (anaerobic). Human actions such as fertiliser runoff, habitat loss, invasive species and climate change disrupt these systems; ecosystems respond with resistance and resilience.
- Ecosystem, Food Chains and Energy Flow – An ecosystem is all the living things in a place plus the non-living things around them, working together. Energy enters as sunlight, passes one way up a food chain, and only about 10% moves to each next level.
- The Carbon Cycle: Where Carbon Is Stored and How It Moves – Carbon moves between the air, living things, soil, oceans and rocks. These places are called stores (or sinks and sources), and the movements are called flows (fluxes). Photosynthesis takes carbon dioxide out of the air; respiration, decomposition and burning put it back. The ocean takes in and gives out huge amounts. Over millions of years carbon is locked into rocks and fossil fuels, and volcanoes and weathering slowly return it. People now burn fossil fuels and clear forests, adding carbon faster than natural sinks can take it up, so the CO₂ in the air rises and the Earth warms.
- Animal Behaviour: Why Animals Do What They Do – Behaviour is everything an animal does in reply to a stimulus from outside (a predator, light, a sound) or inside (hunger, hormones). Some behaviour is innate (instinct, born with it); some is learned (habituation, conditioning, imprinting, insight). Behaviour has a function: it helps the animal survive and reproduce, often by living in groups. Many animals are sentient: they can feel pain, fear and pleasure.
3. Heredity: inheritance and variation of traits
DNA and chromosomes as instructions · Sources of genetic variation · Statistics of trait expression
- Heredity and Mendel's Laws – Heredity is the passing of traits from parents to children through genes. Each parent gives one copy of every gene. A dominant copy hides a recessive one, which is why Mendel saw 3:1 in a monohybrid cross and 9:3:3:1 in a dihybrid cross. Genes are pieces of DNA that make proteins, and proteins build the trait.
4. Biological evolution: unity and diversity
Evidence of common ancestry · Four factors of natural selection · Changes in trait proportions · Adaptation · Environmental change, speciation and extinction · Mitigating threats to biodiversity
- Evolution: How New Kinds of Living Things Arise – Variations arise during reproduction. Nature selects those that help survival, so over many generations populations change: this is evolution. Only inherited (DNA) changes pass on; acquired changes do not. Separated populations can become new species. Homologous organs, analogous organs and fossils help us trace who is related to whom, and complex organs evolved step by step.
- Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).
- Diversity and Classification of Living Organisms – Earth has millions of kinds of living things, and India is one of the richest places. To study them, we sort them into groups by asking simple questions about their bodies: Is there a nucleus? One cell or many? Can it make its own food? This gives five kingdoms: Monera, Protista, Fungi, Plantae and Animalia. Animals split into invertebrates and vertebrates. Every species gets a two-part scientific name. Viruses are not cells, so they fit in no kingdom.