CSEC Biology

Biology is the study of living organisms. It is a broad field covering the minute workings of chemical processes inside our cells to broad scale concepts of ecosystems and global climate change.

There are many subdivisions in biology, including:

• Anatomy
• Botany (plant sciences)
• Marine biology
• Zoology and microbiology
• Biochemistry, genetics, physiology
• Cell biology, developmental biology and ecology

Classification of Living Organisms

All living organisms are classified into groups based on shared characteristics. The current system uses five kingdoms:

Kingdom	Examples	Characteristics
Animalia	Humans, birds, fish, insects	Multicellular, heterotrophic, no cell walls
Plantae	Trees, flowers, grasses	Multicellular, autotrophic (photosynthesis), cell walls of cellulose
Fungi	Yeast, mushrooms, molds	Cell walls of chitin, heterotrophic (absorptive)
Prokaryotae/Monera	Bacteria	Unicellular, no nucleus, cell walls
Protista	Amoeba, algae, seaweed	Mostly unicellular, diverse nutrition methods

The classification hierarchy is: Kingdom → Phylum → Class → Order → Family → Genus → Species.

Organisms are named using the binomial system (e.g., Homo sapiens for humans).

Cells are the basic unit of life. Organisms can be classified as prokaryotes (bacteria) or eukaryotes (animals, plants, fungi, protists).

Cell Structure and Function

Structure	Function
Cell wall	Protects and provides shape (in plants, fungi, bacteria)
Cell membrane	Controls what enters and leaves the cell (selectively permeable)
Nucleus	Contains chromosomes (DNA) which stores hereditary information
Mitochondria	"Power House": site of aerobic respiration
Vacuole	Stores nutrients, wastes or water
Chloroplast	Site of photosynthesis in plants (contains chlorophyll)
Ribosome	Helps in the manufacture of proteins
Endoplasmic Reticulum	Helps in production, processing, and transport of proteins and lipids
Cytoplasm	Site of most chemical reactions

Cell Transport Processes

Diffusion: Movement of particles from high to low concentration until evenly distributed (e.g., gases in lungs).

Osmosis: Movement of water molecules from high to low water concentration through a selectively permeable membrane (e.g., water uptake by root hairs).

Active Transport: Movement of molecules from low to high concentration using energy (ATP) and carrier proteins (e.g., mineral uptake by plant roots).

Deoxyribonucleic acid (DNA) is a complex molecule that contains all information necessary to build and maintain an organism. It serves as the primary unit of heredity.

Chromosomes

Chromosomes are composed of DNA coiled around proteins called histones. Humans inherit 46 chromosomes (23 pairs):

• 22 pairs of autosomes (non-sex chromosomes)
• 2 sex-determining chromosomes (XX in females, XY in males)

Genes

A gene is a segment of DNA that provides coded instructions for synthesis of RNA, which when translated into protein leads to expression of hereditary characteristics.

Birth Process

• Occurs approximately 9 months after fertilization in humans
• The period between fertilization and birth is called the gestation period
• Few weeks before birth, fetus turns head downwards
• Birth begins when uterus muscles start to contract (labour), caused by hormone oxytocin
• Cervix stretches to allow baby's head to pass through
• Muscles push baby downwards and out of mother's body
• Placenta falls from uterus (afterbirth)
• Baby starts breathing independently; umbilical cord is cut

Birth Control Methods

Birth control methods aim to prevent pregnancy but do not prevent STIs. There are three main groups:

Abortion

Abortion is a medical process for ending pregnancy. Reasons include:

• Risk to woman's mental or physical health
• Pregnancy due to crime (e.g., rape)
• Genetic defect of unborn child
• Fear of poverty

It should ideally occur before the 12th week and always under medical supervision.

Effects of Cigarette Smoking

Cigarettes contain approximately 4,000 chemicals, many harmful including tar, nicotine, carbon monoxide, benzene, formaldehyde, and hydrogen cyanide. Over 50 are carcinogenic (cause cancer).

Care of Teeth

1. Proper diet: Calcium, phosphorus, and vitamin D for healthy teeth structure.
2. Fluoride: In toothpaste and mouthwash to harden enamel.
3. Brushing: After every meal to remove food particles that bacteria ferment into acids.
4. Flossing: At least once daily to remove plaque between teeth.

Problems of Circulatory System

Hypertension: High blood pressure (above 120/80 mmHg) often due to artery blockage or loss of elasticity.

Atherosclerosis: Build-up of fat, cholesterol, and other substances in artery walls forming plaques.

Angina: Chest pain when heart muscle doesn't get enough oxygen-rich blood.

Coronary thrombosis: Blood clot in coronary artery causing heart attack.

Movement is a reaction to a stimulus. In plants, it's usually growth movement (phototropism, hydrotropism). In animals, it's locomotion (entire body moves).

Functions of the Human Skeletal System

1. Protection: Skull protects brain; ribs protect heart and lungs.
2. Support: Provides framework for body; allows attachment of organs and muscles.
3. Locomotion: Muscles attached to bones allow movement.
4. Blood formation: Bone marrow produces red blood cells and phagocytes.
5. Storage: Stores calcium and phosphorus.
6. Feeding: Lower jaw of skull in mammals.

Joints

Joints occur where two or more bones meet. There are two main types:

Muscles

The muscular system is responsible for movement. Muscles work in antagonistic pairs:

• Tendons: Connect muscles to bones
• Ligaments: Connect bones to bones
• When biceps contracts (flexion), triceps relaxes (lengthens) to lift arm
• When triceps contracts, biceps relaxes to lower arm