3.2.1 Cell structure paper 1 and 3

Question 1

Define the terms eukaryotic and prokaryotic cell

Answer 1

Eukaryotic - DNA is contained in a nucleus, contains membrane-bound specialised organelles
Prokaryotic - DNA is ‘free’ in cytoplasm, no organelles eg bacteria and archaea

Question 2

State the relationship between an organ system and specialised cells

Answer 2

Specialised cells –> tissues that perform a specific function –> organs made of serveral tissue types –> organ systems

Question 3

Describe the structure and function of the cell-surface membrane

Answer 3

Fluid mosaic phospholipid bilayer with extrinsic intrinsic proteins embedded

Isolates cytoplasm from extracellular environment
Selectively permeable to regulate transport of substances
Involved in cell signalling / cell recognition

Question 4

Explain the role of cholesterol, glycoproteins and glycolipids in the cell-surface membrane

Answer 4

Cholesterol - steroid molecule connects phospholipids and reduces fluidity
Glycoproteins - cell signalling, cell recognition (antigen) and binding cells together
Glycolipids - cell signalling and cell recognition

Question 5

Describe the structure of the nucleus

Answer 5

Surrounded by nuclear envelope, a semi permeable double membrane
Nuclear pores allow substances to enter/exit
Dense nucleolus made of RNA and proteins assembles ribosomes

Question 6

Describe the function of the nucleus

Answer 6

Contains DNA coiled around chromatin into chromosomes
Controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis. semiconservative replication

Question 7

Describe the structure of a mitochondrion

Answer 7

Surrounded by double membrane
Inner on is folded to form cristae: site of electron transport chain
Inside is the fluid matrix - contains mitochondrial DNA, respiratory enzymes, lipids, proteins

Question 8

Describe the structure of a chloroplast

Answer 8

Surrounded by double membrane,
has inside membranes called thlakoids, these are stacked to form grana, which are linked together to form lamellae - thing flat pieces of thylakoid membrane

Question 9

State the function of mitochondria

Answer 9

Site of aerobic respiration to produce ATP

Question 10

State the function of chloroplasts

Answer 10

Site of photosynthesis to convert solar energy to chemical energy

Question 11

Describe the structure and function of the golgi apparatus

Answer 11

Group of fluid filled membrane bound flattened sacs

Processes and packages lipids and proteins
Also makes lysosomes

Question 12

Describe the structure and function of a lysosome

Answer 12

Round organelle surrounded by a membrane, with no clear internal structure

Contains digestive enzymes called lysozymes, kept separate from cytoplasm by membrane
Can be used to digest invading cells or to break down worn out part of cells

Question 13

Describe the structure and function of a ribosome

Answer 13

Formed of protein and RNA, free in cytoplasm or attached to ER

Site where proteins are made

Question 14

Describe the structure and function of the ER

Answer 14

System of membranes enclosing a fluid-filled space.

Rough ER - many ribosomes attached - folds and processes proteins
Smooth ER - synthesises and processes lipids

Question 15

Describe the structure of the cell wall

Answer 15

Rigid structure surrounding cells
Bacteria - made of the polysaccharide murein
Fungi - chitin
Plants - made of cellulose

Question 16

Functions of the cell wall

Answer 16

Mechanical strength and support
Physical barrier against pathogens
Part of apoplast pathway (plants) to enable easy diffusion of water

Question 17

Describe the structure and function of the vacuole in plants

Answer 17

Surrounded by single membrane (tonoplast) found in cytoplasm.
Contains cell sap

Maintains pressure inside cell and keeps it rigid, stops plant wilting
Involved in isolation of unwanted chemicals inside cell

Question 18

Explain some common cell adaptations

Answer 18

Folded membrane or microvilli increase surface area eg for diffusion
Many mitochondria = large amounts of ATP for active transport
Walls one cell thick to reduce distance of diffusion pathway

Question 19

State the role of plasmids in prokaryotes

Answer 19

Small ring of DNA that carries non essential genes
Can be exchanged between bacterial cells via conjunction

Question 20

State the role of flagella in prokaryotes

Answer 20

Rotating tail propels organism

Question 21

State the role of the capsule in prokaryotes

Answer 21

Polysaccharide layer:
Prevents desiccation
Acts as food reserve
Provides mechanical protection against phagocytosis and external chemicals
Sticks cells together

Question 22

Compare eukaryotic and prokaryotic cells

Answer 22

Both have cell membrane, cytoplasm, ribosomes

Question 23

Contrast eukaryotic and prokaryotic cells

Answer 23

Eukaryotic: Larger, no capsule plasmids, DNA contained in nucleus, cellulose cell walls

Prokaryotic: Smaller, no nucleus or membrane bound organelles, circular DNA, murein cell wall

Question 24

Outline what happens during cell fractionation and ultracentrifugation

Answer 24

1. Cells should be placed in a cold, buffered and isotonic solution. (cold - slows down enzyme activity, buffered- prevents proteins denaturing, isotonic - prevents damage to organelles by osmosis), the homogenised to break up the cells
   2.Filter the homogenate to remove cell debris
2. Place in a centrifuge and spin at a low speed
3. Most dense organelles form a pellet with supernatant on top
4. Respin supernatant at higher speed

Question 25

State the order of sedimentation of organelles during differential centrifugation

Answer 25

Nucleus, mitochondria, lysosomes, RER, ribosomes