AQA GCSE Biology Paper 1

Eukaryotic cells

Complex, large cells that contain a nucleus and membrane-bound organelles, including animal and plant cells.

Prokaryotic cells

Simpler and smaller cells that do not have a nucleus, with genetic material in a single circular strand of DNA.

Size of eukaryotic cells

Typically 10-100 micrometres in size.

Size of prokaryotic cells

About 0.1-5 micrometres in size.

Comparison of cell sizes

Prokaryotic cells are often ten to a hundred times smaller than eukaryotic cells.

Nucleus

Contains DNA and controls the cell's activities.

Cytoplasm

Jelly-like substance where most chemical reactions happen.

Cell membrane

Controls what goes in and out of the cell.

Mitochondria

Where aerobic respiration happens, releasing energy.

Ribosomes

Where proteins are made.

Cell wall

Made of cellulose, it strengthens the cell in plants.

Permanent vacuole

Filled with cell sap to support the cell in plants.

Chloroplasts

Where photosynthesis happens; contain chlorophyll to absorb light.

Specialised cells

Cells that are adapted to carry out specific functions.

Sperm cells

Have a tail to swim, lots of mitochondria for energy, and enzymes in the head to digest the egg membrane.

Nerve cells

Long and branched to carry electrical signals quickly.

Muscle cells

Can contract to move the body and contain many mitochondria.

Root hair cells

Have long projections to absorb water and minerals.

Xylem cells

Hollow with thick walls to carry water.

Phloem cells

Transport sugars and have sieve plates for efficient flow.

Cell differentiation

The process by which a cell becomes specialised.

Microscopy

Techniques that allow us to view cells and large organelles.

Light microscope

Used to observe cells, allowing for the viewing of stained specimens.

Order of magnitude calculations

Used to compare sizes of cells, such as a 100-fold difference between eukaryotic and prokaryotic cells.

Electron Microscopes

Provide much greater magnification and resolution, allowing us to see smaller structures like ribosomes, mitochondria, and plasmids.

Magnification Formula

Magnification = Image size ÷ Real size

Unit Conversion

The ability to convert units (e.g., mm to µm) and use standard form for answers.

Example of Magnification

If the image size is 0.002 mm and the real size is 0.000002 mm, the magnification is 1000x.

Chromosomes

Long molecules of DNA found in the nucleus of cells that carry genes controlling characteristics.

Genes

Small sections of DNA that code for proteins.

Human Chromosomes

Human body cells have 46 chromosomes, arranged in 23 pairs.

Cell Cycle

Describes how cells grow and divide, consisting of three stages.

Stages of Cell Cycle

1. Cell growth and increase in sub-cellular structures. 2. DNA replication. 3. Mitosis.

Mitosis

The process where chromosomes line up, are pulled apart, and the nucleus divides, producing two identical daughter cells.

Uses of Mitosis

Growth, repair of damaged tissues, and asexual reproduction.

Stem Cells

Undifferentiated cells that can develop into many other types of cells.

Embryonic Stem Cells

Can become almost any type of human cell and are taken from early embryos.

Therapeutic Cloning

A process where an embryo is made using a patient's DNA to avoid rejection.

Adult Stem Cells

Found in places like bone marrow and can only form certain cells, such as blood cells.

Meristem Stem Cells

Found in plants and can produce any type of plant cell throughout the plant's life.

Risks of Stem Cell Use

Possible transfer of viral infections from donor to patient, ethical objections to destroying embryos, high cost and need for strict controls.

Benefits of Stem Cell Use

Treating diseases like diabetes and paralysis, and producing cloned, disease-free plants.

Diffusion

The spreading out of particles from an area of high concentration to low concentration, occurring in gases and liquids without energy.

Examples of Diffusion

Oxygen diffusing into blood in the lungs, carbon dioxide diffusing out of cells into the blood, urea diffusing from cells into the blood for excretion.

Factors Affecting Diffusion Rate

Concentration gradient, temperature, and surface area.

Exchange Surfaces

Surfaces that increase the effectiveness of exchange by having a large surface area and a thin membrane.

Adapted Surfaces in Animals

Examples include small intestine villi for nutrient absorption, lungs alveoli for gas exchange, and fish gills for oxygen extraction.

Osmosis

The movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane.

Isotonic

The concentration inside the cell is equal to that of the solution, resulting in no change in mass.

Active Transport

The movement of substances against the concentration gradient, from low to high concentration, requiring energy from respiration.

Tissue

A group of similar cells working together to perform a specific function.

Organ

Different tissues working together to perform a specific function.

Organ System

Several organs working together to carry out processes necessary for life.

Human Digestive System

Responsible for breaking down large insoluble food molecules into smaller soluble ones that can be absorbed into the blood.

Amylase

An enzyme in saliva that starts breaking down starch.

Peristalsis

Muscular contractions that push food through the oesophagus to the stomach.

Hydrochloric Acid

A substance in the stomach that helps digest food and creates an acidic environment for enzymes.

Bile

Produced by the liver to neutralise stomach acid and emulsify fats.

Villi

Small, finger-like projections in the small intestine that increase surface area for absorption.

Food Tests

Chemical tests used to identify nutrients in food.

Iodine Solution

Used to test for starch; turns from orange-brown to blue-black if starch is present.

Benedict's Solution

Used to test for sugars; changes from blue to green, yellow, or brick red depending on concentration when heated.

Biuret Solution

Used to test for proteins; a positive result is a purple colour change.

Sudan III

A stain used to test for lipids; creates a red layer on top if fat is present.

Ethanol Emulsion Test

A test for lipids that creates a cloudy white layer if lipids are present.

Enzymes

Biological catalysts that speed up chemical reactions in the body.

Lock and Key Theory

The model explaining how each enzyme is specific to a particular substrate, fitting like a key in a lock.

Active Site

The region of the enzyme where the substrate binds.

Denatured Enzyme

An enzyme that stops working due to a change in the shape of the active site.

Carbohydrases

Enzymes, such as amylase, that break down starch into sugars like maltose.

Proteases

Enzymes, such as pepsin, that break down proteins into amino acids.

Lipases

Enzymes that break down lipids (fats and oils) into fatty acids and glycerol.

Optimum pH

The pH level at which enzymes work best; activity slows outside this range.

Enzyme Reaction Rate Formula

Rate = 1 / time.

Glucose

Used in respiration to release energy.

Amino Acids

Used to make proteins for growth and repair.

Fatty Acids and Glycerol

Used to build cell membranes and make hormones.

Glycogen

Excess glucose that can be stored in the liver and muscles.

Heart

A double pump that circulates blood; the right side pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the body.

Heart Chambers

The heart has four chambers: right atrium, left atrium, right ventricle, and left ventricle.

Blood Flow Direction

Blood flows in one direction due to valves.

Vena Cava

The blood vessel bringing blood from the body.

Pulmonary Artery

Carries blood to the lungs.

Pulmonary Vein

Brings oxygenated blood back from the lungs.

Aorta

Carries blood to the body.

Alveoli

Tiny air sacs in the lungs where gas exchange happens.

Heart Rate Control

Controlled by a group of cells in the right atrium acting as a natural pacemaker.

Artificial Pacemaker

A device fitted to control heart rhythm using electrical signals.

Blood Vessels

Three types: arteries, veins, and capillaries.

Arteries

Carry blood away from the heart under high pressure with thick muscular walls.

Veins

Carry blood towards the heart under low pressure and have valves to stop backflow.

Capillaries

Tiny vessels that allow substances to diffuse in and out of the blood with thin, one-cell-thick walls.

Blood Flow Rate Formula

Rate = volume ÷ time.

Blood Components

Blood is made up of red blood cells, white blood cells, platelets, and plasma.

Red Blood Cells

Carry oxygen using a protein called haemoglobin and are shaped like biconcave discs.

White Blood Cells

Defend against infection and can change shape to engulf pathogens.

Platelets

Small fragments of cells that help blood clot at wounds.

Plasma

The liquid part of blood that carries hormones, carbon dioxide, glucose, and waste products.

Coronary heart disease

Caused by the coronary arteries becoming narrowed by layers of fatty deposits, reducing blood flow to the heart muscle and potentially leading to a heart attack.

Stents

Metal mesh tubes that are inserted to keep the artery open.