Biology Notes

Variety of Living Organisms

Plants:

  • Multicellular, photosynthesis (chloroplasts), cellulose cell walls, store carbohydrates (starch/sucrose).
  • Examples: flowering plants (maize), herbaceous legume (peas/beans).

Animals:

  • Multicellular, no photosynthesis, no cell walls, nervous system, store carbohydrate as glycogen.
  • Examples: mammals (humans), insects (housefly).

Fungi:

  • Multicellular (e.g., mucor): mycelium (hyphae, many nuclei).
  • Some single-celled (e.g., yeast): chitin cell wall.
  • Saprotrophic nutrition.

Protoctists:

  • Microscopic, single-celled.
  • Some like animal cells (Ameoba), some like plant cells (Chlorella).
  • Plasmodium causes malaria.

Prokaryotes and Viruses

Bacteria:

  • Single-celled microorganisms, murein cell wall, no nucleus (circular DNA).
  • Some photosynthetic, most feed off other organisms.
  • Examples: Lactobacillus bulgaricus (yoghurt), Pneumococcus (pneumonia).

Viruses:

  • Non-living, parasitic, reproduce inside host cells only.
  • No respiration, sensitivity, or nutrition.
  • Protein coat enclosing DNA or RNA.
  • Examples: tobacco mosaic virus, HIV.

Cell Parts and Functions

  • Nucleus: DNA, controls cell activities.
  • Cytoplasm: jelly-like, chemical reactions.
  • Cell membrane: selectively permeable.
  • Mitochondria: aerobic respiration (ATP).
  • Rough ER: protein synthesis & transport.
  • Ribosome: protein synthesis.
  • Cell wall (plant): cellulose, shape, turgor pressure resistance.
  • Chloroplasts: photosynthesis, chlorophyll.
  • Vacuole: cell sap (sugars, ions, solutes).

Biological Molecules

Carbohydrates: C, H, O.

  • Monosaccharide (glucose).
  • Disaccharide (sucrose, maltose).
  • Polysaccharide (cellulose, starch, glycogen).
    Fats: C, H, O.
  • Glycerol + 3 fatty acids.
    Proteins: C, H, O, N, S.
  • Amino acids.

Enzymes

  • Biological catalysts (proteins).
  • Affected by temperature: rate increases with temperature up to optimum; denature at high temperatures.

Movement of Substances

  • Diffusion: high to low concentration.
  • Osmosis: water from high to low water potential across a semi-permeable membrane.
  • Active Transport: low to high concentration (against gradient), using energy and carrier proteins.

Factors Affecting Rate of Movement

  1. High concentration gradient.
  2. High temperature.
  3. Large surface area to volume ratio.
  4. Short diffusion distance.

Nutrition in Flowering Plants

  • Autotrophic: photosynthesis (CO2 + H2O using sunlight).
  • Glucose uses: respiration, starch storage, cellulose (cell walls), fats/oils, proteins.

Leaf Structure

  • Waxy cuticle: reduces water loss.
  • Upper epidermis: thin, transparent.
  • Palisade mesophyll: many chloroplasts, light absorption.
  • Spongy mesophyll: air gaps, gas exchange.
  • Lower epidermis: stomata (gas diffusion), guard cells (stomata control).

Limiting Factors of Photosynthesis

  • Light intensity: Rate increases as light increases.
  • CO2CO_2 concentration: Rate increases as concentration increases.
  • Temperature: Rate increases as temperature increases but enzymes denature at high temperatures.

Mineral Requirements

  • Nitrates: amino acids, growth. Deficiency: stunted growth, yellow leaves.
  • Magnesium: chlorophyll. Deficiency: yellow leaves.

Human Nutrition

  • Balanced Diet: nutrients in right amounts, right energy.
    Factors affecting energy needs:
  • Age, activity level, pregnancy
    Nutrients:
  • Carbohydrates, proteins, fats, minerals, vitamins, water, dietary fiber

Human Nutrition Stages

  1. Ingestion: Taking in food.
  2. Digestion: Breaking down food (mechanical & chemical).
  3. Absorption: Movement into blood.
  4. Assimilation: Use by cells.
  5. Egestion: Elimination of undigested material.

Alimentary Canal

  • Peristalsis: Muscle contractions to move food.
  • Mouth: Mechanical (chewing), Chemical (salivary amylase).
  • Oesophagus: Transports food.
  • Stomach: Hydrochloric acid (acidic pH), Pepsin (proteins to amino acids).

Small Intestine

  • Duodenum: Pancreatic & bile juice.
  • Pancreatic juice: Amylase, trypsin, lipase.
  • Bile juice: Neutralizes, emulsifies fats.
  • Ileum: Maltase (maltose to glucose).

Villi Adaptations

  1. Thin walls (single layer of cells).
  2. Microvilli.
  3. Capillary network.
  4. Lacteal vessels.
  5. Many mitochondria (active transport).

Gas Exchange in Humans

Breathing in:

  • Diaphragm contracts, external intercostals contract.
  • Volume increases, pressure decreases.
    Breathing out:
  • Diaphragm relaxes, external intercostals relax, internal intercostals contract.
  • Volume decreases, pressure increases.

Alveoli Adaptations

  1. Large surface area.
  2. Thin walls.
  3. Capillary network.
  4. Ventilated.
  5. Moist.

Lung Protection

  • Ciliated epithelium and goblet cells.
  • Mucus traps bacteria, cilia push it out.

Smoking Consequences

  • Tar damages cilia, increases mucus (bronchitis).
  • Tar damages alveoli (emphysema).
  • Tar causes lung cancer.
  • Carbon monoxide reduces oxygen transport.
  • Nicotine increases heart rate, blood pressure (heart attack risk).

Breathing Rate and Exercise

  • Increases to provide more oxygen and remove carbon dioxide.
  • Anaerobic respiration releases lactic acid.
  • Breathing remains high after exercise to oxidize lactic acid.

Transport in Plants

Xylem:

  • Hollow, dead cells, lignin walls.
  • Transport water & mineral ions, support.
    Phloem:
  • Translocation (sucrose & amino acids from source to sink).

Human Circulatory System

Heart:

  • 4 chambers (atria & ventricles), divided by septum.
    Systemic circulation:
  • Left atrium receives blood from lungs, left ventricle pumps to aorta.
    Pulmonary circulation:
  • Right atrium receives blood from body, right ventricle pumps to pulmonary artery.

Heart Rate

  • Exercise increases heart rate & stroke volume.
  • Adrenaline increases heart rate.

Coronary Heart Disease

  • Cholesterol deposits narrow arteries, less blood flow to heart muscle, leading to heart attack.
  • Causes: smoking, high blood pressure, diet, stress, lack of exercise.

Blood Vessels

Arteries:

  • Strong, elastic walls, narrow lumen to maintain high pressure.
    Veins:
  • Wider lumen, valves to prevent backflow, thin walls.
    Capillaries:
  • Thin walls, large surface area, diffusion.

Blood

  • Plasma: transports nutrients, wastes, hormones.
  • Red blood cells: transport oxygen (haemoglobin, no nucleus, biconcave).
  • White blood cells: phagocytes (engulf pathogens), lymphocytes (antibodies).

Nervous System

  • CNS: brain & spinal cord.
  • Receptors: detect stimuli.
  • Effectors: muscles (contract), glands (secrete).
  • Neurons: sensory, motor, relay.

Reflex Action

  • Automatic, involuntary, rapid response.
  • Bypasses brain.

Eye

  • Cornea: refracts light.
  • Lens: focuses light.
  • Iris: controls pupil size.
  • Retina: light receptors (rods & cones).
    Rods:
  • Dim light, black & white vision.
    Cones:
  • Bright light, color vision.

Pupil Reflex

Bright light:

  • Circular muscles contract, pupil smaller.
    Dim light:
  • Radial muscles contract, pupil larger.
    Skin:
  • Temperature regulation (vasodilation, vasoconstriction, sweating, shivering).

Homeostasis

  • Maintenance of constant internal environment.
  • Hormones: chemical messengers.
  • Adrenaline: increases heart rate, blood pressure, glucose.
  • Insulin: lowers blood glucose.

Plant Coordination

  • Phototropism: growth towards light (auxins).
  • Geotropism: growth towards/away from gravity.

Plant Reproduction

  • Sexual (variation) vs. Asexual (rapid).
  • Insect-pollinated vs. Wind-pollinated flowers.
  • Fertilization: fusion of gametes.
  • Germination: needs warmth, water, oxygen.

Human Reproduction

Female system:

  • Ovary: ova & hormones.
  • Fallopian tube: fertilization.
  • Uterus: implantation.
  • Hormones: estrogen (repair uterus), progesterone (maintain uterus lining).
    Male system:
  • Testis: sperm & testosterone.
  • Scrotum: temperature control.
  • Adaptive features of sperm: tail, mitochondria, acrosome.

Genetics

  • Genome: entire DNA.
  • Chromosome: DNA strand with genes.
  • Gene: DNA section for protein.
  • Alleles: gene variants.
  • Dominant & recessive alleles.
  • Genotype & phenotype.
  • Homozygous & heterozygous.
    Mutation:
  • Change in DNA sequence.

Inheritance

  • Monohybrid (single gene) & polygenic (multiple genes).
  • Sex determination: XX (female), XY (male).
  • Natural selection: survival of advantageous traits.
  • Antibiotic resistance: bacteria evolve resistance.

Cell Division

  • Mitosis: identical daughter cells (growth, repair).
  • Meiosis: non-identical daughter cells (gametes).

Ecology

  • Population, community, habitat, ecosystem.
  • Biotic & abiotic factors.

Energy Flow

  • Food chains & webs.
  • Producers, consumers, decomposers.
  • Trophic levels.
  • Energy loss: heat, movement, excretion.

Cycles

  • Carbon cycle: photosynthesis, respiration, combustion, decomposition.

Human Influences

  • Pollution (sulfur dioxide, carbon monoxide).
  • Greenhouse effect & global warming.
  • Eutrophication.

Resources

  • Food production (greenhouses, fertilizers, pest control).
  • Microorganisms (yeast, lactobacillus).
  • Industrial fermenters: aseptic conditions, agitation, temperature & pH control, oxygenation, nutrition.
  • Selective breeding & genetic engineering.