2.1.1 (g) - Plant and Animal Organelles

The benefit of organelles

• Evolved from deep folds in the surface membrance

• Separated by membranes from cytoplasm

• Compartmentalise the process in each organelle

• Division of labour is more efficient

• Each organelle works to allow the survival the cell

Cell Wall (P) - description

A layer of cellulose outside the plasma membrane. 

It may have holes in it that join adjacent cells called plasmodesmata. An associated thinning of the cell wall at these locations is called a pit.

[In Fungi the cell wall is made of a molecule called chitin]

Cell Wall (P) — function

Allows the cell to become turgid by preventing the cell from bursting.

It determines the shape of the cell when it’s turgid and so provides rigidity.

It is freely permeable.

Plasmodesmata allow the movement of substances between cells without passing across the plasma membrane.

Centrioles/ Centrosome (A) - description

The centrosome consists two centrioles perpendicular to each other.

Each centriole is a tube made of microtubules.

Centrioles/ Centrosome (A) - function

Involved in the assembly and organisation of microtubules – particularly the spindle fibres during cell division

Chloroplasts (P) - description

Double membrane layer around the outside with an internal membrane system suspended in a gel called the stroma as well.

A third membrane is folded into thylakoid discs which form stacks called grana.

70S ribosomes

Chloroplasts (P) - function

The site of photosynthesis

Cytoskeleton (P&A) - description

The cytoskeleton is the network of filaments that extend across the cytoplasm of all cells.

A network of 3 types of protein fibres (microtubules, microfilaments and intermediate fibres)

Cytoskeleton (P&A) - function

• Stabilises cell shape

• Allows organelles to be moved about the cell 

• Allows some cells to move 

• Coordinates the movement of chromosomes in cell division

Cytoplasm/ Cytosol (P&A) - description

Technically termed the cytosol which is the gel within the plasma membrane.

Cytoplasm/ Cytosol (P&A) - function

The site of any reaction that the cell performs that doesn’t occur within an organelle.

Organelles are suspended in the cytosol and molecules can pass through the cytosol from one organelle to another.

Flagella and cilia (A&someP) - description

Thin hair-like structures of the plasma membrane containing cytoplasm and a 9+2 arrangement of microtubules.

• Flagella are longer than cilia.

Flagella and cilia (A&someP) - function

They move in a whip-like way to either move cells or move substances over the surface of cells.

Cilia can be used to move cells or move substances such as mucus out of the lungs.

Flagella move cells (e.g. sperm)

Golgi apparatus/ body (P&A) - description

A collection of flattened sacs called cisternae made of membrane with an inner space called the lumen.

The cis face of the Golgi apparatus faces the RER, the trans face is the other side.

Golgi apparatus/ body (P&A) - function

Modifies proteins and packages them in vesicles for transport around the cell or secretion out of it.

Makes lysosomes

Large permanent vacuole (P) - description

Permanent structure in plants

A large membrane-bound sac. The membrane surrounding it is called the tonoplast and the contents are called cell sap.

Large permanent vacuole (P) - function

Stores water, ions, waste products and a range of other molecules for a variety of functions. 

When it swells due to water entering it causes cells to be turgid, providing support.

Lysosomes (A) - description

A membrane-bound sac that contains strong digestive enzymes — hydrolytic enzymes.

Lysosomes (A) - function

• Used for breaking down faulty organelles or engulfed bacteria.

• Degrade waste products in cells, components then can be re-used.

• Also used in autolysis (programmed cell death).

Microvilli (A) - description

Finger-like projections of the plasma membrane.

Microvilli (A) - function

Increase the surface area of the cell for absorption.

Mitochondria (P&A) - description

Double membrane layer around the outside of a gel called the matrix.

The inner membrane is heavily folded which gives a large surface area called the cristae.

70S ribosomes

Mitochondria (P&A) - function

Site of aerobic respiration to generate ATP for cell functions.

Nuclear envelope (P&A) - description

A double membrane layer containing holes called nuclear pores surrounding the nucleus.

The membrane is continuous with the endoplasmic reticulum membrane.

Nuclear envelope (P&A) - function

Allows the entry and exit of molecules from or into the nucleus.

The nuclear pores control the passage of very large molecules into or out of the nucleus.

Nucleolus (P&A) - description

A dark staining region of the nucleus that is not membrane-bound. It contains a high density of nucleic acids.

Nucleolus (P&A) - function

The site of ribosome production

Nucleus (P&A) - description

Contains DNA as linear chromosomes, surrounded by the nuclear envelope.

Double membrane with pores to release RNA

Nucleus (P&A) - function

Coordinates the functions of the cell and controls the cells’ activities by coding for proteins

e.g. enzymes

Plasma/ cell surface membrane (P&A) - description

A double layer of phospholipids with proteins and cholesterol embedded within it. It surrounds the cell contents.

Plasma/ cell surface membrane (P&A) - function

Thin flexible layer controls entry and exit of materials into a cell.

Has receptor molecules which allow it to respond to hormones.

Ribosomes (P&A) - description

• Made of protein and RNA.

• Not membrane-bound.

• Can be free in the cytoplasm or bound to RER

• Consists of two subunits

• 80S

Ribosomes (P&A) - function

Site of protein synthesis.

Amyloplast (P) - description

A membrane-bound sac containing starch

Amyloplast (P) - function

Acts as a starch store for plants

Rough endoplasmic reticulum (RER) (P&A) - description

A network of tubes or sacs called cisternae surrounded by membrane.

The membrane has ribosomes studded on its external surface.

The space inside is called the lumen or cisternal space

Rough endoplasmic reticulum (RER) (P&A) - function

Proteins fold into their shape within the RER and are transported within the RER before being packaged into transport vesicles.

Smooth endoplasmic reticulum (SER) (P&A) - description

A network of tubes or sacs called cisternae surrounded by membrane.

The membrane does not have ribosomes studded to its external surface.

The space inside is called the lumen or cisternal space.

Smooth endoplasmic reticulum (SER) (P&A) - function

Site of lipid and carbohydrate synthesis.

Vesicle (transport or secretory) (P&A) - description

Small spheres enclosed by a membrane. 

They contain a variety of molecule types depending on their function.

Vesicle (transport or secretory) (P&A) - function

Transport molecules from one organelle to another (e.g. RER to Golgi) or out of the cell (i.e. secreted).

They are also used to embed molecules in the plasma membrane.