1.2 Cell Structure

Question 1

what are prokaryotes?

Answer 1

organisms which lack nucleus

Question 2

what are archaebacteria?

Answer 2

bacteria found in extreme environments (high temps, salt concentrations or pH)

Question 3

what are eubacteria?

Answer 3

traditional bacteria including most known pathogenic forms (eg. E.coli)

Question 4

what are structures usually found in prokaryotes? (9) and what do they do?

Answer 4

cytoplasm - internal fluid of cell
nucleoid - region of cytoplasm where DNA is located (DNA is circular (called genophore))
plasmids - autonomous circular DNA molecules that can be transferred between bacteria (horizontal gene transfer)
ribosomes - complexes of RNA and proteins that are responsible for polypeptide synthesis (70S)
cell membrane - semi-permeable and selective barrier surrounding the cell
cell wall - rigid outer covering made of peptidoglycan (maintains shape and prevents bursting/lysis)
slime capsule - thick polysaccharide layer used for protection against desiccation and phagocytosis
flagella - long projections containing motor protein that enables movement
pili - extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjunction (sex pili)

Question 5

what is binary fission?

Answer 5

form of asexual reproduction used by prokaryotic cells

Question 6

what is the process of binary fission? (3 step)

Answer 6

• circular DNA is copied in response to replication signal
• the two DNA loops attach to the membrane
• the membrane elongated and pinches off (cytokinesis) forming two cells

Question 7

what are eukaryotes?

Answer 7

organisms which contain nucleus

Question 8

how do eukaryotes differ from prokaryotes (overview)? (3)

Answer 8

• more complex structure
• believed to have evolved from prokaryotic cells (via endosymbiosis)
• eukaryotic cells are compartmentalized by membrane-bound structures (organelle) that perform specific roles

Question 9

what four kingdoms can eukaryotes be divided into?

Answer 9

Protista - unicellular organisms/ multicellular organisms without specialised tissue
Fungi - have cell mall made of chitin and obtain nutrients via heterotrophic absorption
Plantae - have cell wall made of cellulose and obtain nutrition autotrophically (photosynthesis)
Animalia - no cell wall and obtain nutrition via heterotrophic ingestion

Question 10

what are organelles universal to both prokaryotes and eukaryotes? (3)

Answer 10

Ribosome
cytoskeleton
plasma membrane

Question 11

what is the function and structure of ribosome?(2)

Answer 11

• 2 subunits made of RNA and proteins (eukaryotes = 80S) (prokaryotes = 70S)
• sit of polypeptide synthesis (translation)

Question 12

what is the function and structure of cytoskeleton?(2)

Answer 12

• filamentous scaffolding within the cytoplasm
• provides internal structure and mediates intracellular transport (less developed in prokaryotes)

Question 13

what is the function and structure of plasma membrane? (2)

Answer 13

• phospholipid bilayer embedded w/ proteins
• semi-permeable and selective barrier surrounding the cell

Question 14

what are organelle found in eukaryotes? (6)

Answer 14

Nucleus
- double membrane structure w/ pores (contains inner region called nucleolus)
- stores genetic material (eg. chromatin) and site of ribosome assembly
Endoplasmic reticulum (ER)
- a membrane network that may be smooth ER or studded w/ ribosome/ rough ER
- transports materials between organelle (SER- lipids RER- proteins)
Golgi apparatus
- assembly of vesicles and folded membranes located near the cell membrane
- involving sorting, string, modification and export of secretory products
Mitochondrion
- double membrane, inner membrane highly folded into internal cristae
- site of aerobic respiration (ATP production)
Peroxisome
- membranous sac containing a variety od catabolic enzymes
- catalyses breakdown of toxic substances and other metabolites
Centrosome
-microtubule organising centre (contains paired centrioles in animal cells not in plant cells)
- radiating microtubules form spindle fibres in cell dividsion

Question 15

what additional organelle do plant cells have? (3)

Answer 15

Chloroplast
- double membrane structure w/ internal stacks of membranous discs (thylakoids)
- site of photosynthesis
Vacuole
- fluid filled internal cavity surrounded y membrane
-maintains hydrostatic pressure (animal cells may have small temporary vacuoles)
Cell walls
- external outer covering made of cellulose
- provides support and mechanical strength

Question 16

What additional organelle do animal cells have? (1)

Answer 16

Lysosome
- membranous sacs filled w/ hydrolytic enzymes
- breakdown/ hydrolysis of macromolecules

Question 17

how do electron microscopes work?

Answer 17

electron beams focused by electromagnets to magnify and resolve microscopic specimens

Question 18

what are the two types of electron microscopes?

Answer 18

transmission electron microscopes (TEM) - generate high resolution cross-sections of objects
scanning electron microscopes (SEM) - display enhanced depth to map the surface of objects in 3D

Question 19

what are 2 advantages of electron microscopes?

Answer 19

• higher range of magnification (can detect smaller structures)
• much higher resolution (provide clearer and more detailed images)

Question 20

what are 3 disadvantages of electron microscopes?

Answer 20

• can’t display living specimens
• can’t display in colour
• expensive

Question 21

what is a micrograph?

Answer 21

a photo/digital image taken through a microscope to show a magnified image of a specimen