Topic 1.2

Question 1

Cytoplasm

Answer 1

internal fluid component of the cell

Question 2

Nucleoid

Answer 2

region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)

Question 3

Plasmids

Answer 3

autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)

Question 4

Ribosomes

Answer 4

complexes of RNA and protein that are responsible for polypeptide synthesis (prokaryote ribosome = 70S)

Question 5

Cell membrane

Answer 5

Semi-permeable and selective barrier surrounding the cell

Question 6

Cell wall

Answer 6

rigid outer covering made of peptidoglycan; maintains shape and prevents bursting (lysis)

Question 7

Slime capsule

Answer 7

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

Question 8

Flagella

Answer 8

Long, slender projections containing a motor protein that enables movement (singular: flagellum)

Question 9

Pili

Answer 9

Hair-like extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)

Question 10

Protista

Answer 10

unicellular organisms; or multicellular organisms without specialised tissue

Question 11

Fungi

Answer 11

have a cell wall made of chitin and obtain nutrition via heterotrophic absorption

Question 12

Plantae

Answer 12

have a cell wall made of cellulose and obtain nutrition autotrophically (via photosynthesis)

Question 13

Animalia

Answer 13

no cell wall and obtain nutrition via heterotrophic ingestion

Question 14

Ribosomes

Answer 14

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 15

Cytoskeleton

Answer 15

Structure: A filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol)

Function: Provides internal structure and mediates intracellular transport (less developed in prokaryotes)

Question 16

Plasma membrane

Answer 16

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

Function: Semi-permeable and selective barrier surrounding the cell

Question 17

Nucleus

Answer 17

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 18

Endoplasmic Reticulum

Answer 18

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 19

Golgi Apparatus

Answer 19

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 20

Mitochondrion

Answer 20

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

Function: Site of aerobic respiration (ATP production)

Question 21

Peroxisome

Answer 21

Structure: Membranous sac containing a variety of catabolic enzymes

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

Question 22

Centrosome

Answer 22

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 23

Chloroplast

Answer 23

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

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

Question 24

Vacuole (large and central)

Answer 24

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

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

Question 25

Cell Wall

Answer 25

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 26

Lysosome

Answer 26

Structure: Membranous sacs filled with hydrolytic enzymes

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

Question 27

TEM

Answer 27

2D- through the object

Question 28

SEM

Answer 28

3D

Question 29

Structure of Phospholipids:

Answer 29

• Consist of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule
• Consist of two non-polar tails (hydrophobic) composed of fatty acid (hydrocarbon) chains
• Because phospholipids contain both hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as amphipathic

Question 30

Arrangement in Membranes:

Answer 30

• Phospholipids spontaneously arrange into a bilayer
• The hydrophobic tail regions face inwards and are shielded from the surrounding polar fluids, while the two hydrophilic head regions associate with the cytosolic and extracellular fluids respectively

Question 31

Properties of the Phospholipid Bilayer:

Answer 31

• The bilayer is held together by weak hydrophobic interactions between the tails
• Hydrophilic / hydrophobic layers restrict the passage of many substances
• Individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility
• This fluidity allows for the spontaneous breaking and reforming of membranes (endocytosis / exocytosis)

Question 32

Integral proteins

Answer 32

permanently attached to the membrane and are typically transmembrane (they span across the bilayer)

Question 33

Peripheral proteins

Answer 33

temporarily attached by non-covalent interactions and associate with one surface of the membrane