Biology and Combined Science Comprehensive Study Notes

Cells and Levels of Organisation

  • Specialised Cells and Processes of Life

    • Different types of cells carry out specific functions. When all cells combine their individual functions, they share out the processes of life.
    • Each cell is dependent on others, and they function collaboratively to support diverse processes in an organism.
    • When cells are specialised, they perform a particular job and develop a distinct shape. These changes in shape enable the cell to carry out its specific function.

  • Red Blood Cell (Erythrocytes)

    • Function: To transport oxygen from the lungs to body tissues and carbon dioxide from body tissues back to the lungs.
    • Nucleus: Lacks a nucleus to increase the surface area available for the absorption of oxygen.
    • Shape: Possesses a bi-concave shape and flexibility, which allows them to pass along small capillaries.
    • Haemoglobin: Contains a red pigment called haemoglobin which carries the oxygen needed for cell respiration to produce energy.

  • Muscle Cell

    • Responsibility: Responsible for contraction when stimulated by a nerve to facilitate movement.
    • Structure: These cells are long and thin, possessing the ability to change their shape when they contract.
    • Mitochondria: They contain large numbers of mitochondria to provide the energy required for muscle contraction.

  • Palisade Cell

    • Function: To manufacture food through the process of photosynthesis.
    • Chloroplasts: Packed with chloroplasts containing chlorophyll for the absorption of light.
    • Structure: They are columnar and closely packed together to increase the surface area for the absorption of sunlight and carbon dioxide (CO2CO_2).

  • Root Hair Cell

    • Function: Responsible for the absorption of water and salts from the soil.
    • Cell Walls: Have thin cell walls to allow water and nutrients to pass easily from the soil into the cell.
    • Surface Area: They are numerous to increase the surface area for absorption. The hair-like projection on each cell penetrates between soil particles to offer a large absorbing surface area.
    • Vacuole: A large vacuole facilitates the absorption and storage of water.

Ecosystems

  • Definition: An ecosystem is a self-contained system of interdependent organisms and their physical environment.

  • Components of an Ecosystem:

    • Physical (Abiotic) Components: Includes all non-living factors such as humidity, temperature, air, soil, water, and light.
    • Biological (Biotic) Components: Includes all living organisms such as fungi, plants, animals, and bacteria.

  • Natural Ecosystems

    • Describes the influence of the environment in determining which organisms survive.
    • Characterized by close interaction between plants and animals and a natural balance of nature.
    • Better-adapted organisms survive to reach maturity and produce offspring.
    • Nutrients are naturally recycled by decomposers.
    • Pests and diseases are part of the natural system; no control measures are taken to limit them.

  • Food Chain

    • A nutritional sequence involving a series of organisms through which energy is transferred.
    • Each organism feeds on and derives energy from the preceding one.
    • Usually originates from producers, specifically green plants.
    • The arrow indicate the direction of energy flow: grass→insects→dragon fly→frog→snake→eagle\text{grass} \rightarrow \text{insects} \rightarrow \text{dragon fly} \rightarrow \text{frog} \rightarrow \text{snake} \rightarrow \text{eagle}.

  • Food Web

    • Consists of plants and animals closely linked by their feeding relationships.
    • An organism may feed on more than one organism and may be a source of food for more than one organism.

  • Pyramid of Biomass

    • Biomass: The amount of living material.
    • In a balanced ecosystem, the biomass of producers should be greater than that of herbivores, whose biomass should be greater than that of carnivores.
    • The amount of energy available for the next trophic (feeding) level decreases as one moves up the pyramid.

  • Energy Loss in Food Chains and Webs

    • The sun is the primary source of energy.
    • Producers at the first trophic level trap energy by photosynthesis (100%100\% energy).
    • Consumers lose a significant amount of energy to the environment as heat and due to life processes like respiration, movement, and excretion.
    • On average, about 90%90\% of energy is lost at each level in a food chain; only about 10%10\% is transferred to the next level.
    • Materials not used or eaten by predators are consumed by decomposers like fungi and bacteria.
    • The number of organisms decreases from one trophic level to another due to the lessening energy availability.

Nutrient Cycles

  • The Carbon Cycle

    • Carbon is recycled as carbon dioxide and is present in all organic compounds.
    • Plants remove CO2CO_2 from the air during photosynthesis to build organic compounds.
    • Animals obtain carbon by eating plant-based organic compounds.
    • CO2CO_2 is released back to the atmosphere through respiration and decay of animals, plants, and microorganisms.
    • Human activities, such as burning fossil fuels, also release CO2CO_2.

  • The Nitrogen Cycle

    • Nitrogen is present in all proteins of plants and animals.
    • Decomposition: When organisms die, proteins are decomposed by fungi and bacteria. The resulting nitrates are reabsorbed by plants.
    • Ammonium Compounds: Wastes reaching the ground are acted upon by soil organisms (worms, millipedes, bacteria, fungi) to create ammonium compounds.
    • Nitrification: Nitrifying bacteria such as Nitrosomonas convert ammonium compounds into nitrites, and Nitrobacter converts nitrites into nitrates, the form in which nitrogen is mainly absorbed by plants.
    • Atmospheric Nitrogen: About 79%79\% of air is Nitrogen.
    • Lightning: A small portion of atmospheric nitrogen is changed into ammonia by lightning, then into ammonium compounds.
    • Nitrogen Fixation: Bacteria called Rhizobium, living in the nodules of leguminous plants, convert nitrogen in the air directly into nitrates.
    • De-nitrification: If aeration is poor, certain bacteria use oxygen from nitrates and release nitrogenous gas back into the air.

Artificial Ecosystems and Biodiversity

  • Artificial Ecosystems

    • Heavily influenced by humans (e.g., monoculture, crop production, animal rearing).
    • Farming destroys equilibrium as the same types of plants are grown over an area.
    • Strict control measures are used for pests and diseases.
    • Nutrients are added via artificial fertilizers.
    • Grazing is controlled via paddocks to prevent overgrazing.

  • Biodiversity

    • Variability within species, between species, and between organisms; a measure of organism variety in different ecosystems.

  • Problems Caused by Limited Biodiversity:

    • Pests and disease outbreaks.
    • Unstable and unbalanced ecosystems.
    • Poor nutrient recycling.
    • Soil infertility.
    • Overgrazing and deterioration of the natural ecosystem.
    • Pollution.

  • Advantages of Biodiversity:

    • Wide variety of food sources.
    • Self-sustenance of the ecosystem.
    • Interdependence.
    • Reduced spread of disease.
    • Provision of shelter, medicine, and resources for mankind.

Plant Nutrition and Photosynthesis

  • External Leaf Structure

    • Waxy Cuticle: Waterproof layer that prevents water loss and protects the leaf.
    • Veins: Transport substances to and from the leaf.
    • Petiole: Attaches leaf to stem; can change the leaf's position to maximize sunlight absorption.
    • Lamina: The thin, flat surface of the leaf providing a large surface area.
    • Margin: The edge of the leaf.

  • Internal Leaf Structure

    • Epidermis: Thin and transparent to allow light through. Contains no chloroplasts except in guard cells. Acts as a protective layer and reduces evaporation.
    • Stomata: Pores for gaseous exchange.
    • Palisade Cells: Main region for photosynthesis; columnar and packed with chloroplasts.
    • Spongy Cells: Spherical and loosely packed with air spaces to allow gaseous exchange.
    • Vascular Bundle: Contains Xylem (brings water and minerals) and Phloem (transports sugars and amino acids via translocation).
    • Guard Cells: Pair of cells surrounding each stoma to control opening and closing.

  • Leaf Adaptations for Photosynthesis

    • Broad, flat shape for sunlight and CO2CO_2 absorption.
    • Thinness allows for short diffusion distances.
    • High chloroplast concentration in palisade cells.
    • Large air spaces in spongy mesophyll for CO2CO_2 diffusion.
    • Branching veins provide water and mineral ions.

  • Factors Affecting Rate of Photosynthesis

    • Light Intensity: Rate increases as light intensity increases. This can be measured by counting oxygen bubbles from a pond weed.
    • Carbon Dioxide Concentration: Increasing CO2CO_2 (e.g., adding sodium hydrogen carbonate) increases the rate.
    • Water: Necessary for chemical reactions. Lack of water causes stomata to close, stopping CO2CO_2 absorption.
    • Chlorophyll: Traps light energy to convert it to chemical energy. Without it, photosynthesis cannot occur.
    • Temperature: Rate increases with temperature up to a point, as it facilitates the combination of CO2CO_2 and hydrogen.

  • Testing for Photosynthesis Products

    • Starch Test:
      1. Boil leaf in water to kill cells.
      2. Boil in alcohol to decolorize (Safety: extinguish flames as alcohol is flammable).
      3. Dip in hot water to soften.
      4. Add iodine solution on a white tile; blue-black color indicates starch.
    • Oxygen Test: Place pond weed under a funnel in water, collect gas in an inverted test tube in sunlight for 4−64-6 hours. A glowing wooden splint will relight in the presence of oxygen.

  • Fate of End Products

    • Glucose: Converted to starch for temporary storage. At night, converted to sucrose for translocation via phloem to roots, stems, or fruits. Also used to make amino acids, cellulose (for cell walls), and lipids.
    • Oxygen: Released as a by-product used for respiration.

Human Nutrition and Balanced Diet

  • Balanced Diet: Contains all essential nutrients in correct proportions.

  • Dietary Components:

    • Carbohydrates: Energy-rich (starch and sugars). Broken down into glucose. Abundant in potatoes, bread, maize, rice. Glucose and fructose occur in fruits.
    • Lipids (Fats and Oils): Supply energy and heat (higher values than carbs). Help absorb vitamins, form cell membranes, and cushion organs. Sources: meat, milk, cheese (animal); sunflower oil, palm oil (plant).
    • Proteins: Growth and repair of tissues, building antibodies, and energy in the absence of carbs. Sources: meat, fish, eggs, nuts, soybeans.
    • Vitamins:
      • Vitamin A (Retinol): Sight, skin health, infection fighting. Sources: green vegetables, liver, palm oil.
      • Vitamin C (Ascorbic Acid): Healthy teeth/gums, wound healing, protein metabolism. Sources: citrus fruits, tomatoes, guava.
      • Vitamin D (Calciferol): Bone and teeth formation. Skin produces it in sunlight. Sources: milk, egg yolk.
    • Mineral Salts:
      • Iodine: For thyroxin hormone (growth control). Sources: iodised salt.
      • Calcium: Strong bones/teeth, muscle contraction, blood clotting. Sources: milk, cheese, hard water.
      • Iron: Formation of haemoglobin. Sources: red meat (liver/kidney), spinach, whole grains.
    • Dietary Fibre: Cellulose; aids bowel movement, prevents constipation, binds with cholesterol. Sources: vegetables, whole wheat bread.
    • Water: Makes up about 70%70\% of tissue. Solvent for transport, reactant in digestion, and regulates temperature via sweating.

  • Nutrition for Different Groups

    • Toddler: Needs extra protein for tissue growth. Avoid excessive starchy food to ensure enough protein intake. Needs calcium and iron.
    • Adolescent: Needs increased protein, calcium, Vitamin D, and phosphates for rapid growth and bone development.
    • Manual Worker: High energy requirement. Needs balanced diet with high energy foods, more salts, and water to replace losses from sweating.
    • Sedentary Worker: Needs less energy-giving food to avoid obesity. Focus on variety of vegetables and fruits.

The Alimentary Canal and Digestion

  • Ingestion: Intake of food through the mouth. Teeth (32 in an adult) chop and grind food. Saliva moistens food and contains salivary amylase (starch to maltose).

  • Types of Teeth:

    • Incisors (8 total): Chisel-shaped for biting and cutting. Single root.
    • Canines: Pointed for gripping and tearing. Single root.
    • Premolars: Flat with cusps for crushing and grinding. Two roots.
    • Molars: Largest teeth for grinding and crushing.

  • Digestion Types:

    • Mechanical: Physical breakdown (chewing, stomach churning, bile emulsification).
    • Chemical: Enzymes break large insoluble molecules into small soluble ones.

  • Processes in the Gut:

    • Peristalsis: Involuntary rhythmic contraction of circular and longitudinal muscles pushing food along the oesophagus.
    • Stomach: Churns food into chyme. Gastric juice contains Hydrochloric acid (kills bacteria, provides pH for pepsin), Rennin (coagulates milk), Pepsin (proteins to polypeptides), and Mucus (protects stomach lining).
    • Small Intestine (Duodenum): Pancreatic juice and bile are added. Pancreatic amylase (starch to maltose), Trypsin (proteins to peptides/amino acids), Pancreatic lipase (fats to fatty acids and glycerol). Bile (from liver) emulsifies fats and neutralizes acid.
    • Small Intestine (Ileum): Completion of digestion. Secrete Maltase (maltose to glucose), Sucrase (sucrose to glucose/fructose), Lipase, and Trypsin.

  • Absorption and Assimilation:

    • Absorption: Taking soluble substances into the blood. The ileum is long with villi (finger-like projections) to increase surface area. Villi have thin epithelium and dense capillary networks. Fatty acids/glycerol enter the lacteal.
    • Large Intestine: Colon absorbs water and Vitamin B (produced by bacteria from fiber). Undigested matter (faeces) passes to the rectum.
    • Assimilation: Utilization of nutrients. Glucose is oxidized for energy (ATPATP). Fats build cell membranes. Amino acids build proteins; excess is deaminated in the liver to form glycogen and urea.
    • Egestion: Elimination of undigested waste via the anus.

Malnutrition and Deficiency Diseases

  • Malnutrition Disorders:

    • Obesity: Caused by high carbohydrate intake stored as fat. Increased risk of heart disease and type 2 diabetes.
    • Anorexia Nervosa: Self-starvation leading to heart failure, muscle loss, and dehydration.
    • Diabetes Mellitus Type 2: Result of obesity and lack of exercise.

  • Deficiency Diseases:

    • Kwashiorkor: Lack of protein; enlarged abdomen, swollen liver. Treated with high protein diet (dried skimmed milk).
    • Goitre: Lack of iodine; swelling of the thyroid gland. Prevented by iodised salt.
    • Scurvy: Lack of Vitamin C; joint pain, dry skin, tooth loss. Treated with citrus fruits.
    • Anaemia: Lack of iron; inability to make haemoglobin leading to weakness/tiredness.
    • Night Blindness: Lack of Vitamin A.
    • Beriberi: Lack of Vitamin B1.

  • Food Tests Summary:

    • Starch: Iodine solution (Blue-black).
    • Reducing Sugar: Benedict’s solution + heat (Green/Orange to Red/Brown precipitate).
    • Proteins: Sodium hydroxide + 1%1\% Copper sulphate (Purple color).
    • Fats: Ethanol + water (Cloudy white emulsion).

Respiratory System

  • Alveoli Adaptations for Gaseous Exchange:

    • Globular/sac-like shape for large surface area.
    • Moist surfaces to dissolve gases.
    • Thin walls (one cell thick) for easy diffusion.
    • Extensive capillary network to maintain concentration gradients.

  • Inhaled vs. Exhaled Air:

    • Oxygen: Inhaled 21%21\%, Exhaled 16%16\%.
    • Carbon Dioxide: Inhaled 0.03%0.03\%, Exhaled 4%4\%.
    • Moisture: Inhaled variable, Exhaled saturated.
    • Temperature: Inhaled cool, Exhaled warm.

  • Respiration:

    • Aerobic: Total oxidation of glucose with oxygen.
    • Formula: glucose+oxygen→carbon dioxide+water+energy (ATP)\text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water} + \text{energy (ATP)}.
    • Anaerobic: Breakdown of glucose without oxygen; less energy released.
    • In animals: glucose→lactic acid+little energy\text{glucose} \rightarrow \text{lactic acid} + \text{little energy}.
    • In yeast: glucose→carbon dioxide+alcohol+energy\text{glucose} \rightarrow \text{carbon dioxide} + \text{alcohol} + \text{energy}.

Transport Systems

  • Transpiration in Plants:

    • Loss of water vapour. Factors increasing rate: high temperature, low humidity, air movement (wind), high light intensity, large surface area, and high number of stomata.
    • Potometer: Instrument to measure water uptake/loss. Formula: rate of transpiration=distance moved by air bubbletime in seconds\text{rate of transpiration} = \frac{\text{distance moved by air bubble}}{\text{time in seconds}}.
    • Plant adaptations to reduce transpiration: sunken stomata, hairs, thick cuticles, rolled leaves, fewer stomata on upper surfaces.

  • Turgidity and Plasmolysis:

    • Turgidity: Cell is expanded due to water absorption; Turgor pressure supports plant shape.
    • Plasmolysis: Protoplasm shrinks away from the cell wall due to water loss by osmosis in a concentrated solution. Leads to wilting.

  • Transport in Humans:

    • Double Circulatory System: Blood flows through the heart twice (Pulmonary and Systemic loops).
    • Blood Functions: Transport (CO2CO_2, O2O_2, nutrients, waste, hormones, heat), Homeostasis, and Defence (WBCs and platelets).
    • Arteries: Thick walls, elastic fibers, narrow lumen, high pressure, no valves.
    • Veins: Thin walls, large lumen, low pressure, valves present to prevent backflow.
    • Capillary: Walls one cell thick, very small lumen, permeable for diffusion.

Reproduction

  • Plant Reproduction:

    • Seed Structure:
      • Maize (Monocot): One cotyledon, endosperm for food, has pericap.
      • Bean (Dicot): Two cotyledons (food store), has testa.
    • Germination Conditions: Water/Moisture (medium for reactions), Suitable Temperature (20∘C20^{\circ}C to 40∘C40^{\circ}C for enzymes), and Oxygen (for aerobic respiration).
    • Germination Success: percentage germination=number of seeds germinatednumber of seeds planted×100\text{percentage germination} = \frac{\text{number of seeds germinated}}{\text{number of seeds planted}} \times 100.
    • Asexual (Vegetative) Reproduction: Rhizomes (grass), Tubers (potato), Cuttings (cassava, sweet potato). Advantages: no gametes needed, identical to parent. Disadvantages: crowding, no genetic variation.

  • Human Reproduction:

    • Male: Testes (produce sperm and testosterone), Scrotum (temperature regulation), Epididymis (storage), Sperm duct, Prostate/Cowper’s/Seminal vesicles (add secretions to activate sperm), Urethra, Penis.
    • Female: Ovaries (produce ova, oestrogen, and progesterone), Oviduct (fertilisation site), Uterus (implantation site), Cervix, Vagina.
    • Sex Cells: Sperm is small, motile (mitochondria), and has an acrosome (enzymes). Ovum is larger, non-motile, with food reserves.
    • Menstrual Cycle: Approximately 2828 days. Day 1−51-5: Menstruation. Day 6−136-13: Uterus lining builds (oestrogen). Day 1414: Ovulation (LHLH surge). Day 15−2815-28: Progesterone maintains lining.
    • Pregnancy: Fertilization forms a zygote, then a ball of cells called a blastula. Implantation occurs in the endometrium. After 88 weeks, embryo becomes a fetus. Placenta act as a barrier and exchange organ (nutrients/oxygen to fetus, waste/CO2CO_2 from fetus).

  • Contraception Methods:

    • Natural: Abstinence, Rhythm method (monitoring temperature/days 11−1711-17).
    • Barrier: Condoms (latex sheath), Diaphragm (rubber dome).
    • Intra-Uterine Device (IUD): Plastic/copper device preventing implantation; can last 55 years.
    • Chemical: Spermicides (foams/jellies).
    • Hormonal: Oral pill (suppresses ovulation), Injection (Depo-Provera, effective for 1212 weeks).

Health and Diseases

  • Sexually Transmitted Infections (STIs):

    • Chancroid: Bacterium Haemophilus ducreyi; soft painful ulcers.
    • Gonorrhoea: Bacterium Neisseria gonorrhorae; pain during urination, yellowish discharge, can cause sterility/blindness in newborns.
    • Syphilis: Bacterium Treponema Pallidum; three stages (Chancre →\rightarrow Rash →\rightarrow Nerve/Heart damage).
    • Genital Herpes: Herpes Simplex Virus (HSV); itching sores, fever, no cure.
    • HIV/AIDS: Spread via body fluids; attacks T-helper lymphocytes. Managed by Anti-Retroviral drugs (ARVs).

  • Infectious/Communicable Diseases:

    • Malaria: Caused by Plasmodium falciparum via female Anopheles mosquito. Lifecycle involves liver and red blood cells. Symptoms: high fever (41∘C41^{\circ}C), shivering.
    • Cholera: Bacterium Vibrio cholerae; rice watery stools, severe dehydration. Treated with Oral Rehydration Therapy (ORT).
    • Ebola: Virus spread by contact; incubation 2−212-21 days. Symptoms: internal/external bleeding, organ failure.
    • Typhoid: Bacterium Salmonella typhosus; stomach ulcers, rash, white coating in mouth.

  • Substance Abuse:

    • Tobacco: Nicotine (addiction), Tar (lung cancer, destroys cilia), Bronchitis.
    • Alcohol: CNS depressant, liver cirrhosis, slows reaction times.
    • Solvents (Glue/Benzene): Hallucinations, brain damage.
    • Cannabis/Mandrax: Mania, hallucinations, safety risks.

  • Immunity:

    • Active Immunity: Body produces its own antibodies. Natural (after infection) or Artificial (vaccination).
    • Passive Immunity: Ready-made antibodies transferred. Natural (placenta/breast milk) or Artificial (serum).
    • Zimbabwe Immunization Schedule: BCG (birth), DPT/Polio (3,4,53, 4, 5 months), Measles (99 months), Booster (1818 months), Vitamin A every 66 months up to 55 years.