cells

Question 1

what is the modern cell theory?

Answer 1

1. cell is the smallest living unit in all organisms
2. all living things are made out of cells - have basic features in common, differences between cells are due to the addition of extra features=provides indirect evidence for evolution
3. all cells come from other pre-existing cells - prokaryotic/eukaryotic

Question 2

what causes a eukaryotic cell?

Answer 2

from mitosis or meiosis

Question 3

what are the groups of eukaryotic cells?

Answer 3

-fungi
-animal
-plants
-protists
(algal and fungal cell are similar to plant cells)

Question 4

what are the distinguishing features of eukaryotic cells?

Answer 4

• cytoplasm containing membrane-bound organelles
• so DNA enclosed in a nucleus

Question 5

what are the structures found in animal cells?

Answer 5

• cell membrane
  -mitochondrion
  -nucleus
  -ribosomes
  -rough endoplasmic reticulum (RER)
  -Smooth endoplasmic reticulum (SER)
  -Golgi apparatus and vesicles
  -lysosomes

Question 6

what are the structures found in a plant cell?

Answer 6

• cell membrane
  -mitochondrion
  -nucleus
  -ribosomes
  -rough endoplasmic reticulum (RER)
  -Smooth endoplasmic reticulum (SER)
  -Golgi apparatus and vesicles
  -lysosomes
  -chloroplast
  -cell wall
  -cell vacuole

Question 7

diagram of a plant and animal cell with labelled structures

Answer 7

Question 8

describe the structure of the cell surface membrane

Answer 8

• found in all cells phospholipid bilayer embed within and attached on the outside (proteins, carbohydrates and cholesterol)
  -hydrophilic phosphate heads - point to/are attracted to water
  -hydrophobic fatty acid tails - point away/repelled from water

Question 9

describe the function of the cell-surface membrane

Answer 9

• ## selectively permeable so enables control of passage of substance in/out of cellmolecules/receptors/antigens on surface allows cell recognition/signalling

Question 10

describe the structure of the nucleus

Answer 10

-nuclear envelope: double membrane that surrounds the nucleus - controls entry/exit of materials
-nuclear pores: allow passage of larger molecules (typically 3000 pores in each nucleus)
-nucleoplasm: granular, jelly like material that makes up the bulk of the nucleus
-nucleolus(dense region): manufactures ribosomal rRNA and assembles the ribosomes (may be more than 1 in a nucleus)
-chromosomes(highly condensed)/ chromatin (condensed) : consists of protein/histone-bound, linear DNA

Question 11

describe the function of a nucleus

Answer 11

• holds/stores genetic information which codes for polypeptide (proteins) in the form of DNA and chromosomes
  -site of DNA replication
• site of transcription (part of protein synthesis) producing mRNA
  -control centre of the cell through the production of MRN + tRNA + hence protein synthesis

Question 12

describe the structure of ribosomes

Answer 12

-not a membrane bound organelle
-made of ribosomal RNA and protein ( two subunits)- 80s found in eukaryotic cells, 70s found in prokaryotic cells
- occur in vast numbers - 25% of the dry mass of a cell

Question 13

describe the function of a ribosome

Answer 13

• site of protein synthesis

Question 14

describe the structure of rER and sER

Answer 14

-both have folded membranes called cisternae
-rER has ribosomes on cisternae (outer membrane)
-lacks ribosomes on surface, more tubular in appearance

Question 15

describe the function of rER + sER

Answer 15

-rER: ribosomes on surface provides a larger surface area for the synthesis of proteins and glycoproteins. provides pathway for transport of materials inside rER e.g. proteins
- sER: synthesises/store/ transport and processes lipids + carbohydrates
e.g. cholesterol and steroid hormones

Question 16

describe the structure of Golgi apparatus and Golgi vesicles

Answer 16

-Golgi apparatus: flattened membrane sacs
- Golgi vesicles: small membrane sac

Question 17

describe the function of Golgi apparatus and Golgi vesicles

Answer 17

Golgi apparatus:
-modifies protein, e.g. adds carbohydrates to produce glycoproteins
- modifies lipids, e.g. adds carbohydrates to make glycolipids
- packages proteins/ lipids into Golgi vesicles
-produces lysosomes (a type of Golgi vesicles)

Golgi vesicles:
-transports proteins/lipids to their required destination
- e.g. moves to and fuses with cell-surface membrane

Question 18

describe the structure of lysosomes

Answer 18

• bags of digestive enzymes
• has a membrane
• has hydrolytic enzymes

Question 19

describe the function of lysosomes

Answer 19

-release hydrolytic enzymes (lysozymes) to break down/hydrolyse pathogens or worn out cell components (organelles) for reuse of materials
- hydrolyse phagocytic cells e.g. white blood cells+ bacteria

Question 20

describe the structure of mitochondria

Answer 20

• double membrane that controls the entry/exit of material
• inner membrane is folded to form extension of cristae: provides a larger surface area for the attachment of enzymes and other proteins involved in respiration
• matrix: contains proteins, lipids, ribosomes(70s) and circular DNA which allows the mitochondria to control the production of their own proteins

Question 21

describe the function of mitochondria

Answer 21

• site of aerobic respiration
• to produce ATP for energy release (energy carrier molecule)
  -e.g. for protein synthesis/vesicle movement/active transport

Question 22

describe the structure of chloroplasts in plants and algae

Answer 22

• chloroplast envelope: double plasma membrane that surrounds the organelle- highly selective in what can be entered/exit the chloroplast
  -grana: stacks of thylakoid (folded membranes embedded with photosynthetic pigment called chlorophyll where the first stage of photosynthesis takes place
  -lamella: thylakoids linking grana
  -stroma: fluid filled matrix where the second stage of photosynthesis takes place. contains thylakoid membranes, small 70s ribosomes, circular DNA and within the stroma are a number of other structures e.g. starch granules and lipid droplets