Biology

Importance of biology

• It helps us understand our own bodies and stay healthy.
• It is the basis of medicine, agriculture and conservation.
• It explains the relationship between living things and the environment.

Laboratory safety

• Follow the teacher's instructions at all times.
• Do not taste or smell chemicals carelessly.
• Report any accident immediately and keep the bench clean.

Aims of first aid

• To preserve life.
• To prevent the condition from getting worse.
• To promote recovery.

Common first-aid measures

Clean and cover wounds to stop bleeding and infection; cool burns with clean water; support and immobilise a fractured limb; place an unconscious but breathing person in the recovery position.

Personal hygiene

Keeping the body, clothes and surroundings clean prevents many diseases. This includes regular bathing, washing hands before eating, and proper disposal of waste.

Disease prevention

• Communicable diseases spread from one person to another (e.g. cholera, malaria).
• Prevention includes vaccination, clean water, good sanitation and balanced diet.

Why classify?

Classification makes the study of the huge variety of living things easier, shows relationships between organisms, and gives each a recognised scientific name.

The taxonomic hierarchy

Organisms are grouped from the largest unit to the smallest: Kingdom, Phylum, Class, Order, Family, Genus and Species.

Parts of a cell

• Cell membrane — controls what enters and leaves the cell.
• Cytoplasm — where chemical reactions occur.
• Nucleus — controls the activities of the cell.
• Plant cells also have a cell wall, chloroplasts and a large vacuole.

Levels of organisation

Cells form tissues, tissues form organs, organs form systems, and systems together make a complete organism.

Diffusion and osmosis

Diffusion is the movement of particles from a region of high concentration to a region of low concentration. Osmosis is the diffusion of water across a semi-permeable membrane from a dilute to a more concentrated solution.

Active transport

Active transport moves substances against the concentration gradient and therefore requires energy. It is important for absorption of mineral salts by roots and nutrients in the gut.

The five kingdoms

• Monera — single-celled organisms without a true nucleus (bacteria).
• Protista — mostly single-celled with a true nucleus (amoeba).
• Fungi — feed by absorption (mushrooms, yeast).
• Plantae — make their own food by photosynthesis.
• Animalia — feed on other organisms.

Photosynthesis

Green plants make their own food using carbon dioxide and water in the presence of sunlight and chlorophyll, producing glucose and oxygen. The word equation is: carbon dioxide + water → glucose + oxygen.

Balanced diet and digestion

A balanced diet contains carbohydrates, proteins, fats, vitamins, mineral salts, water and roughage in the right proportions. Digestion breaks down complex food into simple soluble substances that the body can absorb.

Transport in plants

Xylem vessels carry water and mineral salts from the roots to the leaves; phloem carries manufactured food from the leaves to other parts of the plant.

Transport in humans

Blood is pumped by the heart through arteries, veins and capillaries. It carries oxygen, food, hormones and wastes, and helps fight disease.

Gaseous exchange

In humans, gaseous exchange occurs in the lungs (alveoli); in plants it occurs through stomata in leaves and lenticels in stems.

Aerobic and anaerobic respiration

• Aerobic respiration uses oxygen and releases much energy: glucose + oxygen → carbon dioxide + water + energy.
• Anaerobic respiration occurs without oxygen and releases less energy (e.g. fermentation by yeast).

Excretory organs

• Kidneys — remove urea and excess water and salts as urine.
• Lungs — remove carbon dioxide and water vapour.
• Skin — removes excess water and salts as sweat.

Homeostasis

The body keeps factors such as temperature, water and blood sugar within narrow limits so that cells can work efficiently.

Nervous coordination

The nervous system (brain, spinal cord and nerves) carries fast electrical messages. A reflex action is a rapid, automatic response that protects the body.

Hormonal coordination

Endocrine glands release hormones into the blood to bring about slower, longer-lasting responses, e.g. insulin controls blood sugar.

Functions of the skeleton

• Support and shape of the body.
• Protection of delicate organs.
• Provision of surfaces for muscle attachment.
• Movement at joints.

Muscles and joints

Muscles work in antagonistic pairs: as one contracts the other relaxes, pulling bones to move at a joint, e.g. the biceps and triceps at the elbow.

Types of reproduction

Asexual reproduction involves one parent and produces identical offspring; sexual reproduction involves the fusion of male and female gametes and produces varied offspring.

Reproduction in plants

In flowering plants, pollination transfers pollen to the stigma, fertilisation forms a seed, and the ovary develops into a fruit.

Conditions for growth

• A supply of food (nutrients).
• Water.
• Suitable temperature.
• Oxygen for respiration.

Measuring growth

Growth can be measured by increase in height, mass or number of cells, and is often shown on a growth curve.

Key terms

• Gene — a unit of inheritance carried on a chromosome.
• Dominant trait — one that shows even when only one allele is present.
• Recessive trait — one that shows only when both alleles are present.

Monohybrid cross

A monohybrid cross follows the inheritance of a single characteristic. A Punnett square is used to show the possible combinations of alleles in the offspring.

Natural selection

Individuals with features best suited to the environment survive and reproduce, passing on those features. Over many generations this changes the characteristics of a population.

Evidence for evolution

• Fossils show how organisms have changed over time.
• Similarities in anatomy of related species.
• Comparative embryology and molecular evidence.

Key terms

• Habitat — the place where an organism lives.
• Population — organisms of the same species in an area.
• Ecosystem — a community of organisms together with their non-living environment.

Energy flow

Energy flows from the sun to producers (green plants), then to consumers along a food chain. At each level much energy is lost, so food chains are usually short.

Care of the reproductive system

Good hygiene, a balanced diet, regular medical check-ups and avoiding risky behaviour help maintain reproductive health.

Preventing STIs and HIV/AIDS

• Abstaining from sex, or being faithful to one uninfected partner.
• Avoiding sharing sharp objects and unscreened blood.
• Seeking early treatment and counselling.