Biology 2025

DNA Shape

double-helix

What is DNA made up of?

nucleotides

Nucletide

1 sugar, 1 phosphate, 1 base

Sugar shape

pentagon

Phosphate shape

small circle

Chromosomes in humans

46 chromosomes (23 pairs).

Sex chromosomes - Female

XX

Sex chromosomes - Male

XY

Sexual reproduction

Involves two parents and produces genetic variation using meiosis.

Asexual reproduction

Asexual involves one parent and produces identical offspring, using mitosis.

Punnett square

It predicts the probability of offspring inheriting particular traits based on the alleles from each parent

Natural selection

The process where organisms best adapted to their environment survive and reproduce, passing on their traits.

Digestive system

Breaks down food into nutrients for absorption.

What order does the digestive system go in?

Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus

Enzymes

A biological chemical that speeds up/completes a reaction

Chemical digestion

Uses enzymes to break food into new, simpler substances.

Physical digestion

Breaks food into smaller pieces — no new substances made.

Respiratory system

Exchanges oxygen and carbon dioxide between the body and air.

What order does the respiratory system go in?

Nose / Mouth → Trachea → Bronchi →Bronchioles → Alveoli

What does the diaphram do?

Helps pull air into the lungs when they contract.

What happens in the alveoli?

Exchange of oxygen and carbon dioxide.

What happens during diffusion in the body?

Oxygen moves from alveoli to blood, and carbon dioxide moves from blood to alveoli.

Circulatory System

Carries substances like oxygen, nutrients, and waste around the body

What are the three main parts of the circulatory system?

Heart, blood vessels, blood

What does the heart do?

Acts as a pump to move blood around the body

What sends signals to make the heart beat?

The brain (electrical impulses)

How many chambers does the heart have?

Four – two atrium and two ventricles

What do valves in the heart do?

Stop blood from flowing backward

Which side of the heart pumps blood to the lungs?

Right

Which side of the heart pumps blood to the rest of the body?

Left

What are the two main blood circuits?

Pulmonary circuit and systemic circuit

What does the pulmonary circuit do?

Takes deoxygenated blood to the lungs and brings oxygenated blood back

What does the systemic circuit do?

Carries oxygenated blood to the body and brings deoxygenated blood back

What do arteries do?

Carry blood away from the heart

What do veins do?

Carry blood toward the heart

What are capillaries?

Tiny vessels where gas and nutrients are exchanged

What are the four main parts of blood and their jobs?

Red blood cells: carry oxygen; White blood cells: fight infection; Platelets: clot blood; Plasma: carries nutrients, hormones, and waste

Cellular respiration equation

Sugar + Oxygen —> carbon dioxide + water + energy