Cell Structure

What are organelles?

Organelles are specialised structures inside cells that carry out particular functions.

What are membrane-bound organelles?

Membrane-bound organelles are organelles surrounded by one or more membranes.

What are non-membrane-bound organelles?

Non-membrane-bound organelles are cell structures that are not surrounded by membranes.

What is ultrastructure?

Ultrastructure is the detailed internal structure of a cell that can be seen using an electron microscope.

Why is an electron microscope used to view ultrastructure?

An electron microscope has a much higher resolution than a light microscope, allowing much smaller cell structures to be seen.

Give six examples of membrane-bound organelles.

Nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, and lysosomes.

Give three examples of non-membrane-bound organelles.

Ribosomes, centrioles, and the cytoskeleton.

What is the plasma membrane?

The plasma membrane, also called the cell-surface membrane, is the boundary around a cell that controls exchange between the cell and its environment.

What is the main function of the plasma membrane?

It controls the movement of substances into and out of the cell.

What role do receptor molecules in the plasma membrane have?

Receptors allow cell recognition and enable cells to respond to chemical signals.

What is the nucleus?

The nucleus is a membrane-bound organelle that contains the cell’s genetic material and controls the cell’s activities.

What does the nucleus contain?

The nucleus contains genetic material in the form of DNA, arranged as chromatin or chromosomes.

What is chromatin?

Chromatin is loosely coiled DNA associated with proteins in the nucleus.

What is the nuclear envelope?

The nuclear envelope is the double membrane that surrounds the nucleus.

How many membranes make up the nuclear envelope?

The nuclear envelope is made of two membranes.

What are nuclear pores?

Nuclear pores are openings in the nuclear envelope that allow substances to move between the nucleus and cytoplasm.

What substances can leave the nucleus through nuclear pores?

RNA can leave the nucleus through nuclear pores.

What is the nucleolus?

The nucleolus is a dense region inside the nucleus where ribosomal RNA is made and ribosomes are assembled.

What is the role of the nucleolus?

The nucleolus makes ribosomal RNA and assembles ribosomes.

What are mitochondria?

Mitochondria are rod- or sausage-shaped organelles that are the site of aerobic respiration.

What is the main function of mitochondria?

Mitochondria produce ATP during aerobic respiration.

What is ATP?

ATP, adenosine triphosphate, is the immediate energy source used by cells.

How many membranes surround a mitochondrion?

A mitochondrion has a double membrane: a smooth outer membrane and a folded inner membrane.

What are cristae?

Cristae are the folds of the inner mitochondrial membrane.

Why are cristae important?

Cristae increase the surface area available for the reactions of aerobic respiration and ATP production.

Why do cells with high energy demands contain many mitochondria?

They require large amounts of ATP, so they need a high rate of aerobic respiration.

What is the endoplasmic reticulum?

The endoplasmic reticulum is a network of membrane-bound flattened sacs and tubules that is continuous with the nuclear envelope.

What are the two types of endoplasmic reticulum?

Rough endoplasmic reticulum and smooth endoplasmic reticulum.

What is rough endoplasmic reticulum?

Rough endoplasmic reticulum, or RER, is endoplasmic reticulum with ribosomes attached to its outer surface.

Why does rough endoplasmic reticulum look rough?

It looks rough because ribosomes are attached to its surface.

What is the main function of rough endoplasmic reticulum?

RER synthesises, folds, processes, and transports proteins, especially proteins for secretion or use in membranes.

What is the role of ribosomes on rough endoplasmic reticulum?

Ribosomes carry out protein synthesis by joining amino acids together to make polypeptides.

What is smooth endoplasmic reticulum?

Smooth endoplasmic reticulum, or SER, is endoplasmic reticulum without ribosomes attached.

Why does smooth endoplasmic reticulum look smooth?

It has no ribosomes attached to its surface.

What is the main function of smooth endoplasmic reticulum?

SER synthesises and transports lipids, including lipids used to make steroid hormones.

Which organelle is important in the synthesis of lipids and steroid hormones?

Smooth endoplasmic reticulum.

What is the Golgi apparatus?

The Golgi apparatus is a stack of flattened membrane-bound sacs, called cisternae, usually located near the nucleus.

What does the Golgi apparatus receive?

The Golgi apparatus receives proteins and lipids from the endoplasmic reticulum in transport vesicles.

What is the main role of the Golgi apparatus?

The Golgi apparatus modifies, sorts, and packages proteins and lipids into vesicles for transport or secretion.

How can the Golgi apparatus modify a protein?

It can add carbohydrate groups to a protein, forming a glycoprotein.

What is a glycoprotein?

A glycoprotein is a protein with one or more carbohydrate groups attached.

What are Golgi vesicles?

Golgi vesicles are membrane-bound sacs that transport processed proteins or lipids to their destination in or outside the cell.

Which organelles form lysosomes?

Lysosomes are formed from Golgi vesicles.

What are lysosomes?

Lysosomes are membrane-bound vesicles containing hydrolytic, or digestive, enzymes.

What type of enzymes do lysosomes contain?

Lysosomes contain hydrolytic enzymes.

What do hydrolytic enzymes do?

Hydrolytic enzymes break large molecules into smaller molecules by hydrolysis.

What is one role of lysosomes in a cell?

Lysosomes digest pathogens that have been engulfed by the cell.

How do lysosomes remove worn-out organelles?

Lysosomes release hydrolytic enzymes that break down old, damaged, or redundant organelles.

What is autolysis?

Autolysis is the self-destruction of a damaged or diseased cell when lysosomal enzymes are released.

How can lysosomes contribute to the destruction of a whole cell?

Lysosomal enzymes can be released and digest the cell’s own components.

What is the cytoskeleton?

The cytoskeleton is a network of protein fibres in the cytoplasm that supports the cell and helps organise cell contents.

What are the two main types of cytoskeleton fibre in these notes?

Microtubules and microfilaments.

What are microtubules?

Microtubules are hollow protein tubes that help maintain cell shape and move organelles, chromosomes, and other cell contents.

What do microtubules do during cell division?

Microtubules form spindle fibres that move chromosomes during cell division.

What are microfilaments?

Microfilaments are thin protein fibres that support the cell and are involved in cell movement.

What is the overall function of the cytoskeleton?

The cytoskeleton provides strength, maintains cell shape, positions and moves organelles, and contributes to cell movement and division.

How does the cytoskeleton help determine cell shape?

Its protein fibres provide an internal framework that supports and maintains the cell’s shape.

What role does the cytoskeleton have in organelle movement?

It provides tracks along which organelles and vesicles can be moved within the cell.

What are centrioles?

Centrioles are non-membrane-bound structures made of microtubules.

What is the role of centrioles?

Centrioles help organise spindle fibres during cell division.

What are cilia?

Cilia are short, hair-like extensions from the cell surface that can move substances across the surface of a cell.

What are flagella?

Flagella are longer, whip-like extensions from the cell surface that move the whole cell.

What is the difference between cilia and flagella?

Cilia are usually short and numerous and move substances over a cell surface, whereas flagella are longer and usually move the whole cell.

What is an example of cilia moving substances?

Cilia in the airways move mucus containing trapped dust and pathogens towards the throat.

What is an example of a flagellum moving a cell?

A sperm cell uses its flagellum to swim towards an egg cell.

What internal structure do eukaryotic cilia and flagella contain?

Eukaryotic cilia and flagella contain microtubules arranged in a 9+2 pattern.

Why are cilia and flagella important?

They enable movement of cells or movement of substances across cell surfaces.

What is the difference between a eukaryotic cell and a prokaryotic cell?

Eukaryotic cells have a nucleus and membrane-bound organelles, whereas prokaryotic cells do not.

Which cells contain chloroplasts?

Plant cells and algal cells contain chloroplasts.

What is the main function of chloroplasts?

Chloroplasts are the site of photosynthesis.

What is the main function of ribosomes?

Ribosomes are the site of protein synthesis.

What is the difference between free ribosomes and ribosomes on RER?

Free ribosomes usually make proteins used inside the cell, whereas ribosomes on RER make proteins for secretion, membranes, or lysosomes.