cell structure and organisation

What are the three main principles of cell theory?

1. All living organisms are made of one or more cells.

2. The cell is the basic unit of structure and function in organisms.

3. All cells arise from pre-existing cells by division.

Name two types of cells.

Prokaryotic cells (no nucleus or membrane-bound organelles) and eukaryotic cells (have a nucleus and membrane-bound organelles).

What is the function of the nucleus?

Contains DNA organised into chromosomes; controls cell activities by regulating gene expression

What is the nucleolus and what does it do?

A dense region inside the nucleus where ribosomal RNA is produced and ribosome subunits are assembled.

Describe the structure and role of mitochondria.

Double-membrane organelles with a folded inner membrane (cristae) and a matrix containing enzymes — site of aerobic respiration and ATP production.

What is the function of the rough endoplasmic reticulum (RER)?

Studded with ribosomes; synthesises and transports proteins.

What is the smooth endoplasmic reticulum (SER) used for?

Synthesises and transports lipids and steroids; lacks ribosomes.

What does the Golgi apparatus do?

Modifies, packages, and transports proteins and lipids into vesicles for secretion or use within the cell.

What are lysosomes?

Vesicles containing digestive enzymes (e.g. lysozymes) that break down worn-out organelles or pathogens.

What is the structure and function of ribosomes?

Small organelles made of rRNA and protein; site of protein synthesis.

What is the role of centrioles?

In animal cells, they form the spindle fibres used in cell division.

Describe the structure of the plasma (cell surface) membrane.

A phospholipid bilayer with embedded proteins — controls the movement of substances in and out of the cell.

What is the plant cell wall made of?

Cellulose microfibrils — provides structural support and prevents bursting from osmotic pressure.

What is the middle lamella?

A pectin-rich layer that cements adjacent plant cells together

What are plasmodesmata?

Small cytoplasmic channels through cell walls that allow transport and communication between plant cells.

Describe the structure and function of chloroplasts.

Double-membrane organelles containing thylakoids stacked into grana within a fluid stroma; site of photosynthesis.

What is the vacuole and what does it do?

A membrane-bound sac filled with cell sap; maintains turgor pressure and stores ions and organic compounds.

Name key features of a prokaryotic cell.

No nucleus; DNA is circular and free in cytoplasm; small ribosomes (70S); cell wall made of murein; sometimes have plasmids, flagella, or capsules.

How does a bacterial cell differ from a plant cell?

Bacteria lack a nucleus and membrane-bound organelles; their cell wall is made of murein instead of cellulose.

What is a plasmid?

A small circular DNA molecule separate from the main chromosome; often carries genes for antibiotic resistance.

What is the difference between magnification and resolution?

Magnification is how much larger the image appears; resolution is the ability to distinguish two close points as separate

What type of image does a light microscope produce?

A colour image of living or dead specimens, up to about ×1500 magnification.

What are the two main types of electron microscopes?

Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM).

How does a TEM work and what is its advantage?

Electrons pass through a thin specimen to produce a 2D image with very high resolution.

How does a SEM work and what does it show?

Electrons bounce off the specimen’s surface to give a detailed 3D image of surface structure.

Why must specimens in an electron microscope be in a vacuum?

So electrons are not scattered by air molecules.

Why can’t living cells be viewed under an electron microscope?

They must be placed in a vacuum and chemically fixed, which kills them.

What is a tissue?

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

What is an organ?

A structure made of different tissues working together to carry out a particular job.

What is an organ system?

A group of organs that cooperate to perform a major body function, such as digestion or respiration.

Give an example of a specialised animal cell and its adaptation

Red blood cells — biconcave shape and no nucleus to increase surface area for oxygen transport.

Give an example of a specialised plant cell and its adaptation.

Palisade mesophyll cells — packed with chloroplasts to maximise light absorption for photosynthesis.

What is cell fractionation used for?

To separate organelles based on density for microscopic or biochemical study.