cell bio aqa gcse

Cell structure

The basic components and organisation of cells, including differences between eukaryotic and prokaryotic cells.

Eukaryotic cell

A cell with a true nucleus enclosed by a membrane, such as animal and plant cells.

Prokaryotic cell

A cell without a true nucleus, where genetic material is free in the cytoplasm, such as bacterial cells.

Nucleus

The control centre of the cell containing genetic material (DNA) that directs cell activities and reproduction.

Cytoplasm

A gel-like substance where most chemical reactions occur, containing enzymes and organelles.

Cell membrane

A partially permeable barrier that controls the movement of substances in and out of the cell.

Mitochondria

Organelles where aerobic respiration takes place, releasing energy from glucose.

Ribosomes

Small structures where proteins are synthesised.

Cell wall (plant cells)

A rigid structure made of cellulose that provides support and protection.

Chloroplast (plant cells)

Organelle containing chlorophyll where photosynthesis occurs.

Permanent vacuole (plant cells)

A fluid-filled sac containing cell sap that helps maintain turgor pressure.

Chromosomal DNA (bacterial cells)

A single loop of DNA in the cytoplasm that carries genetic information.

Plasmid (bacterial cells)

Small, circular rings of DNA that can carry additional genes, such as for antibiotic resistance.

Flagellum (bacterial cells)

A tail-like structure used for movement in some bacteria.

Slime capsule (bacterial cells)

A protective layer around some bacteria that helps prevent drying out or attack.

Subcellular structures

The components inside a cell, including organelles like the nucleus, mitochondria, and ribosomes.

Cell specialisation

The process where cells develop specific structures to perform particular functions.

Sperm cell

Specialised for reproduction with a tail for swimming, acrosome to penetrate the egg, and many mitochondria for energy.

Nerve cell

Specialised for transmitting electrical impulses with a long axon, dendrites for connections, and myelin sheath for insulation.

Muscle cell

Specialised for contraction with contractile proteins, many mitochondria, and a multinucleate structure.

Root hair cell

Specialised for absorption with a large surface area from hair-like projections and thin walls.

Xylem vessel

Specialised for water transport as hollow, lignified tubes without end walls for continuous flow.

Phloem sieve tube

Specialised for transporting sugars with sieve plates and companion cells for support.

Cell differentiation

The process by which a cell becomes specialised for a specific function, involving changes in gene expression.

Microscopy

The use of microscopes to view small objects like cells.

Light microscope

A microscope using light to magnify specimens up to about 1500x, with lower resolution than electron microscopes.

Electron microscope

A microscope using beams of electrons for higher magnification (up to 2,000,000x) and resolution, revealing subcellular details.

Magnification

The factor by which an image is enlarged, calculated as image size divided by actual size.

Resolution

The shortest distance between two points that can be distinguished as separate, determining detail clarity.

Standard form

A way to express very large or small numbers, e.g., 0.0005 m as 5 x 10^-4 m, used in cell size calculations.

Required practical - microscopy

Use a light microscope to observe, draw, and label plant and animal cells; calculate magnification.

Cell division

The process by which cells reproduce, including mitosis for growth and repair.

Chromosome

A thread-like structure in the nucleus made of DNA and proteins, carrying genes.

DNA

Deoxyribonucleic acid, the molecule that carries genetic information in chromosomes.

Cell cycle

The series of stages a cell goes through, including growth (G1), DNA synthesis (S), further growth (G2), and mitosis (M).

Mitosis

A type of cell division producing two genetically identical daughter cells from one parent cell, used for growth, repair, and asexual reproduction.

Binary fission

The process by which prokaryotic cells (bacteria) divide, involving DNA replication and splitting into two.

Stem cell

An undifferentiated cell that can divide to produce more stem cells or differentiate into specialised cells.

Embryonic stem cell

Stem cells from early embryos that can differentiate into any cell type.

Adult stem cell

Stem cells found in tissues like bone marrow, capable of differentiating into a limited range of cell types (e.g., blood cells).

Meristem

Plant tissue containing stem cells, found in roots and shoots, allowing continuous growth.

Therapeutic cloning

Creating embryonic stem cells genetically identical to a patient for treating diseases without rejection.

Ethics of stem cells

Concerns include destruction of embryos for embryonic stem cells; benefits include potential cures for diseases like paralysis.

Transport in cells

The movement of substances across cell membranes.

Diffusion

The net movement of particles from an area of high concentration to low concentration, down a concentration gradient; passive process.

Factors affecting diffusion

Concentration gradient, temperature, surface area to volume ratio, and distance.

Surface area to volume ratio

The relationship explaining why small cells are more efficient for diffusion; larger organisms need transport systems.

Osmosis

The diffusion of water molecules across a partially permeable membrane from high water potential (dilute) to low water potential (concentrated).

Water potential

A measure of the tendency of water to move; pure water has the highest potential.

Turgid

A plant cell full of water, with the vacuole pushing against the cell wall, providing support.

Flaccid

A plant cell that has lost water, becoming soft.

Plasmolysis

When a plant cell loses so much water that the cytoplasm shrinks and pulls away from the cell wall.

Active transport

The movement of particles against a concentration gradient, from low to high, requiring energy from respiration.

Examples of active transport

Root hair cells absorbing minerals from dilute soil; gut cells absorbing glucose from low concentration in intestines.

Required practical - osmosis

Investigate the effect of sugar solutions on plant tissue (e.g., potato cylinders) by measuring mass change to determine osmosis.

Culturing microorganisms

Growing bacteria or other microbes in a controlled environment for study.

Agar plate

A petri dish with nutrient agar gel used to grow bacterial cultures.

Aseptic technique

Methods to prevent contamination, such as sterilising equipment, working near a flame, and sealing plates.

Inoculation

Transferring bacteria to agar using a sterile loop.

Incubation

Keeping cultures at a set temperature (e.g., 25°C in schools to avoid pathogens) for growth.

Zone of inhibition

Clear areas around antibiotic discs where bacteria cannot grow, measuring effectiveness.

Bacterial growth calculation

Number of bacteria = initial number × 2^(number of divisions); divisions every 20-30 minutes under ideal conditions.