Cell ultrastructure

Question 1

Prokaryotic cells

Answer 1

Bacterial cells without membrane-bounded organelles

Question 2

Eukaryotic cells

Answer 2

Cells with membrane-bounded organelles and a distinct nucleus

Question 3

Plasma membrane

Answer 3

The cell membrane separates the contents of the cel from its external environment, and regulates the movement of substances into and out of the cell. Most organelles have their own membrane, enabling separate compartments for specialised membranes

Question 4

Nucleus

Answer 4

The nucleus contains the cell’s DNA and controls the activities. The nuclear membrane contains nucleoplasm, chromatin (diffuse DNA) and the nucleolus, and it has pores to allow materials (such as messenger RNA) out of the cell. The nucleolus manufactures ribosomal RNA and assembles ribosomes

Question 5

Mitochondria

Answer 5

Mitochondria are double membraned organelles, with the inner membrane folded to give cristae. Enzymes associated with aerobic respiration are attached to the cristae. Mitochondria are common in cells which need a lot of energy, such as muscle and epithelial cells

Question 6

Endoplasmic reticulum

Answer 6

A system of membranes enclosing flattened sacs called cisternae. The ER is continuous with the outer nuclear membrane

Question 7

Rough ER

Answer 7

The rough ER has ribosomes on the outer surface of its membranes, and provides a large surface area for making proteins and glycoproteins. It also provides a pathway for the transport of materials

Question 8

Smooth ER

Answer 8

The smooth ER lacks ribosomes and is more tubular in shape. Its role is to synthesise and store lipids and carbohydrates

Question 9

Ribosomes

Answer 9

Small cytoplasmic granules found in the cytoplasm and associated with rough ER. They consist of two subunits (one large, one small) containing ribosomal RNA and protein. Ribosomes are involved in protein synthesis

Question 10

Golgi apparatus

Answer 10

The Golgi apparatus have a similar structure to smooth ER, but more compact. They consist of a stack of flattened, membrane bound sacs (cisternae) surrounded by smaller pinched off vesicles. They process, sort and send on proteins, and create gylcoproteins

Question 11

Lysosomes

Answer 11

Vesicles pinched off the Golgi apparatus containing digestive enzymes, which often fuse together to form membrane bound vacuoles. They digest worn out organelles, break down dead cells (autolysis), break down material ingested by phagocytes (white blood cells) and fuses with cell surface membranes, releasing enzymes to digest material outside the cell

Question 12

Microvilli

Answer 12

Finger-like projections of the cellular membrane that increase the surface area for absorption