1.2 Ultrastructure of cells

Question 1

Prokaroytes

Answer 1

organisms whose cells lack a nucleus

Question 2

Structure of prokaryotes

Answer 2

prokaryotes don’t have a membrane bound structure, a.k.a. organelles.

Question 3

Cell wall

Answer 3

Structure: External outer covering made of cellulose (not an organelle per se, but a vital structure)

Function: Provides support and mechanical strength; prevents excess water uptake

Question 4

Plasma membrane

Answer 4

Structure: Phospholipid bilayer embedded with proteins (not an organelle per se, but a vital structure)

Function: Sem-permeable and selective barrier surrounding the cell

Question 5

Ribosomes

Answer 5

Structure: Two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S)

Function: Site of polypeptide synthesis (this process is called translation)

Question 6

Cytoplasm

Answer 6

Place of metabolic activity.

Question 7

Mesosome

Answer 7

Place of respiration and energy production.

Question 8

Pili

Answer 8

Hairs to protect the cell wall and for DNA exchange with other prokaryotes.

Question 9

Flagellum

Answer 9

Protein structure to cause locomotion.

Question 10

Nucleoid

Answer 10

The area where naked DNA exists. Note that the DNA is single and circular.

Question 11

Plasmid

Answer 11

DNA that can be exchanged.

Question 12

Slime layer

Answer 12

A thick polysaccharide layer used for protection against dessication (drying out) and phagocytosis

Question 13

How do prokaryote cells divide?

Answer 13

Binary fission

Question 14

Outline the process of binary fission

Answer 14

The circular DNA is copied in response to a replication signal
The two DNA loops attach to the membrane
The membrane elongates and pinches off (cytokinesis), forming two cells

Question 15

Cellular components in prokaryote cells

Answer 15

Cytoplasm
Nucleoid
Plasmids
Ribosomes 70s
Cell membrane
Cell wall
Slime capsule
Flagella
Pili

Question 16

Organelles in eukaryote cells

Answer 16

Ribosomes 80S
Cytoskeleton
Plasma membrane
Nucleus
Endoplasmic Reticulum
Golgi Apparatus
Mitochondrion
Peroxisome
Centrosome

Question 17

Plant-cell only organelles

Answer 17

Chloroplast
Vacuole
Cell wall

Question 18

Animal cell only organelles

Answer 18

Lysosome

Question 19

Nucleus

Answer 19

Structure: Double membrane structure with pores; contains an inner region called a nucleolus

Function: Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly

Question 20

Endoplasmic reticulum

Answer 20

Structure: A membrane network that may be bare (smooth ER) or studded with ribosomes (rough ER)

Function: Transports materials between organelles (smooth ER = lipids ; rough ER = proteins)

Question 21

Golgi Apparatus

Answer 21

Structure: An assembly of vesicles and folded membranes located near the cell membrane

Function: Involved in the sorting, storing, modification and export of secretory products

Question 22

Mitochondrion

Answer 22

Structure: Double membrane structure, inner membrane highly folded into internal cristae

Function: Site of aerobic respiration (ATP production)

Question 23

Peroxisome

Answer 23

Structure: Membranous sac containing a variety of catabolic enzymes

Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites

Question 24

Centrosome

Answer 24

Structure: Microtubule organising centre (contains paired centrioles in animal cells but not plant cells)

Function: Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)

Question 25

Chloroplast

Answer 25

Structure: Double membrane structure with internal stacks of membranous discs (thylakoids)

Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids

Question 26

Vacuole

Answer 26

Structure: Fluid-filled internal cavity surrounded by a membrane (tonoplast)

Function: Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)

Question 27

Lysosome

Answer 27

Structure: Membranous sacs filled with hydrolytic enzymes

Function: Breakdown / hydrolysis of macromolecules (presence in plant cells is subject to debate)