Core Concepts of Life Science and Biology Fundamentals

Posted on Dec 2, 2025 in Biology

Photosynthesis: The Process of Life

  • Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (light + chlorophyll)
  • Location: In chloroplasts (mainly leaf cells).
  • Purpose: Converts light energy into chemical energy (glucose).
  • Reactants: Carbon dioxide (from air), water (from roots).
  • Products: Glucose (used/stored), oxygen (released).
  • Uses of Glucose:
    • Respiration (energy)
    • Stored as starch
    • Cellulose (cell walls)
    • Fats and oils (seeds)
    • Proteins (with nitrates)
  • Limiting Factors: Light intensity, temperature, CO₂ concentration, water, and chlorophyll.

Testing for Starch (Evidence of Photosynthesis)

Procedure using Iodine Solution:

  1. Take a leaf exposed to sunlight.
  2. Boil in water (kills cells).
  3. Boil in alcohol (removes chlorophyll).
  4. Rinse in warm water (to soften the leaf).
  5. Add iodine solution →
    • Blue-black: Starch present (photosynthesis occurred).
    • Brown/yellow: No starch (no photosynthesis).

Plant Transport and Nutrition

Vascular Tissue Functions

  • Xylem: Transports water and minerals upwards (via transpiration pull).
  • Phloem: Transports sugars (glucose) both directions (via translocation).
  • Root Hair Cells: Absorb water (osmosis) and minerals (active transport).

Main Mineral Salts and Their Functions

Essential minerals for plant health:

  • Magnesium: Needed to make chlorophyll.
  • Potassium: Most needed by the roots (e.g., for enzyme activation).
  • Phosphorus: Helps turn glucose into energy (ATP production).
  • Nitrogen: Helps damaged plants repair (essential for proteins).

Biological Interdependence

Plants and animals depend on each other for gas exchange, energy flow, and recycling of nutrients.

Basic Cell and Genetic Structure

A cell contains a nucleus, which holds chromosomes. DNA carries all genetic information and contains genes, where each gene controls one specific trait of an organism.

The Excretory System and Kidney Function

Excretion: Purpose and Organs

  • Purpose: To remove wastes (urea, excess salts/water) and control water balance.
  • Main Organs: Kidneys, lungs (CO₂ removal), skin (sweat), liver.
  • Kidney Failure Treatment: Dialysis or transplant.

Detailed Kidney Function Steps

  1. Blood Enters: Dirty blood from the body enters the kidneys through the renal artery.
  2. Filtration: In tiny parts of the kidney called nephrons, waste, water, and small molecules are filtered out of the blood (occurs in the glomerulus).
  3. Reabsorption: The kidneys take back useful substances like glucose, water, and salts into the blood.
  4. Water Balance: Controlled by the hormone ADH, which increases water reabsorption when the body is dehydrated.
  5. Urine Formation: The leftover waste and extra water become urine (contains urea, water, salts, but no glucose or protein).
  6. Urine Transport: Urine travels through tubes called ureters into the bladder, where it is stored before leaving the body via the urethra.

Genetics and Inheritance

Variation within a Species

  • Variation Types:
    • Genetic: Inherited (e.g., eye color, blood group).
    • Environmental: Caused by surroundings (e.g., language, scars).
    • Combined: Influenced by both (e.g., height, weight, skin tone).
  • Continuous Variation: Gradual changes across a range (e.g., height).
  • Discontinuous Variation: Clear, distinct groups (e.g., blood type).

Chromosomes and Genes

  • Chromosomes: Made of DNA, located in the nucleus.
  • Gene: A segment of DNA controlling a specific trait.
  • Allele: A different form of a gene.
  • Human Cells: Contain 46 chromosomes (23 pairs).
  • Sex Chromosomes: XX (female), XY (male).

Fertilization and Inheritance

  • Fertilization: Sperm + egg → zygote.
  • Genotype: Genetic makeup (e.g., Aa).
  • Phenotype: Physical expression of traits (e.g., tall).
  • Dominant Allele: Trait is shown with only one copy present.
  • Recessive Allele: Trait is shown only when two copies are present.
  • Punnett Square: Used to predict offspring traits.

Fetal Growth and Development

  • Development Stages: Zygote → embryo → fetus.
  • Placenta: Facilitates the exchange of gases, nutrients, and waste between mother and fetus.
  • Amniotic Fluid: Cushions and protects the baby.

Natural Selection and Evolution

  • Definition: The process where organisms with beneficial traits survive and reproduce more successfully.
  • Steps of Natural Selection:
    1. Variation exists in the population.
    2. Some individuals have advantageous traits.
    3. They survive longer and reproduce more.
    4. Their genes spread throughout the population.
    5. Over time, the species evolves.

Ecology and Population Dynamics

  • Population: The number of individuals of a single species in a given area.
  • Population Size Changes:
    • Increase: Births, immigration.
    • Decrease: Deaths, emigration.
  • Carrying Capacity: The maximum number of individuals an environment can sustainably support.
  • Causes of Extinction: Habitat loss, hunting, pollution, disease, climate change.
  • Conservation Methods: Protected areas, reforestation, breeding programs.

Scientific Method and Experimental Design

Key Data Terms

  • Range: The difference between the highest and lowest values in a data set.
  • Mean: The average value.

Case Study: Fertilizer and Plant Growth

Question: Does artificial fertilizer affect plant growth?

Hypothesis:

Plants given fertilizer will grow taller and have greener leaves than plants without fertilizer.

Variables

  • Independent Variable: Fertilizer dose (None / Low / High).
  • Dependent Variables: Plant height (cm) and leaf color/number.
  • Controlled Variables: Same species, pot size, soil, water, light, temperature, starting size.

Method (Brief)

  1. Use 3 groups: Control (0 dose), Low dose, High dose — 5 plants per group.
  2. Put all plants in identical pots with the same soil.
  3. Apply fertilizer weekly at set doses. Water equally.
  4. Measure height (cm) and count leaves every 4 days for 3–4 weeks.
  5. At the end, compare average height and leaf counts between groups.

How to Measure and Check Results

  • Measure height from the soil surface to the top of the stem (use the same person each time for consistency).
  • For leaf color, use simple scoring: 1 = pale, 2 = normal, 3 = very green.
  • Calculate the mean height for each group and compare (a bigger mean indicates more growth).

Essential Biology Definitions

  • Ecosystem: A community of living things and the non-living things (like water, air, and soil) that they interact with.
  • Adaptation: A feature that helps an organism survive and reproduce in its environment.
  • Evolution: The slow change of living things over a long time as they adapt to their environment.
  • Natural Selection: When the organisms best suited to their environment survive and pass on their genes to their offspring.
  • Population: A group of the same species living in the same area.
  • Inheritance: The process by which traits are passed from parents to offspring through genes.
  • Gamete: A sex cell (sperm or egg) that joins during fertilization to form a new organism.