Topic 1

What is a cell?

The smallest unit of life that can carry out all vital functions.

Name the levels of organisation in a multicellular organism.

Cell → tissue → organ → organ system → organism.

What is a tissue?

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

What is an organ?

A structure made of different tissues working together.

Function of the nucleus?

Contains genetic material and controls cell activities.

Function of cytoplasm?

Where most chemical reactions occur.

Function of the cell membrane?

Controls movement of substances in and out of the cell.

Function of mitochondria?

Site of aerobic respiration; releases energy.

Function of ribosomes?

Protein synthesis.

What extra structures do plant cells have?

Cell wall

Function of the cell wall?

Supports and strengthens the cell.

Function of chloroplasts?

Site of photosynthesis; contain chlorophyll.

Function of the permanent vacuole?

Maintains turgor pressure to keep the cell rigid.

What are enzymes?

Biological catalysts made of proteins.

What does a catalyst do?

Speeds up chemical reactions without being used up.

What is the active site?

The region of an enzyme where the substrate binds.

Describe the lock-and-key model.

The substrate fits exactly into the enzyme’s active site.

Describe the induced-fit model.

The active site changes shape to fit the substrate.

Why does temperature affect enzyme activity?

High temperatures denature enzymes by changing their shape.

What is enzyme denaturation?

Permanent change in shape so the enzyme no longer works.

How does pH affect enzymes?

Each enzyme has an optimum pH; extremes denature it.

What is diffusion?

Movement of particles from high to low concentration.

Is diffusion passive or active?

Passive (no energy required).

Give two factors that increase diffusion rate.

Larger concentration gradient; higher temperature.

What is osmosis?

Diffusion of water through a partially permeable membrane from high to low water concentration.

What is a partially permeable membrane?

Allows small molecules like water to pass through.

What happens to an animal cell in a hypotonic solution?

It swells and may burst (lysis).

What happens to a plant cell in a hypotonic solution?

Becomes turgid.

What happens to a plant cell in a hypertonic solution?

Becomes plasmolysed.

What is active transport?

Movement of substances against the concentration gradient using energy.

Why is active transport important in roots?

Allows uptake of mineral ions from dilute soil.

Why is surface area to volume ratio important?

Determines how efficiently substances can diffuse in and out.

Why do larger organisms need specialised exchange surfaces?

Their surface area to volume ratio is too small for diffusion alone.

What is magnification?

How many times larger an image is than the real object.

Formula for magnification?

Magnification = image size ÷ actual size

Units commonly used in microscopy?

mm

Why stain cells?

To make structures easier to see.