chapter 1: cellular structure and function

Question 1

state the 3 tenets of cell theory

Answer 1

1. all organisms are composed of cells
2. cells are the basic unit of structure and organisation in organisms
3. all cells come from pre-existing cells

Question 2

3 differences between prokaryotes and eukaryotes

Answer 2

prokaryotes:
- no membrane-bound organelles
- singular circular loop of DNA
- simple w/ little organisation
- typically smaller in size
eukaryotes:
- has membrane bound organelles
- multiple linear strands of DNA
- complex w/ specialisation
- typically larger in size

Question 3

the link between structure and function of cells

Answer 3

• they are related
• the structure, shape and size of a cell determines its specific function
• eg. nerve cells are long and thin as its function is to send messages around the body

Question 4

key differences between plant and animal cells

Answer 4

• plant has a more rigid rectangular shape while animals have a circular rounded shape
• plant cells have cells walls and chloroplasts while animal cells have no cell wall or chloroplast
• plant cells are more closer together, animal cells are more spread out
• plants have one large central vacuole, animals have multiple small vacuoles

Question 5

the relationship between cell size and SA:V ratio

Answer 5

the smaller the cell size, the larger the SA:V

Question 6

ways cells shape can also affect SA:V

Answer 6

• longer and flatter cells can increase SA:V

- foldings of the plasma membrane can also increase the surface area to volume ratio

Question 7

how does SA:V affect the movement of substances into or out of the cell

Answer 7

• the larger the SA:V ratio, the more efficient the cell will be able to carry out its physiological needs
• the ability of a cell to meet its physiological needs is determined by the surface area of the cell.
• the physiological needs of a cell are determined by the cell’s volume
• larger SA means more substances can move in or out more efficiently because there is more area to do so, enabling the cell to meet its physiological needs
• this increases the efficiency of the cell to gain essential nutrients and expel wastes

Question 8

why do cell functions need to be completed by specialised organelles

Answer 8

the specialisation of organelles enables them to efficiently carry out their SPECIFIC function

Question 9

function of nucleus

Answer 9

holds and protects dna

Question 10

function of ribosomes

Answer 10

builds up proteins, protein synthesis (makes proteins)

Question 11

function of rough ER

Answer 11

• internal transport and protein modification - synthesises more complex proteins
• are coated with ribosomes, so protein made in ribosomes can efficiently enter the RER to be modified
• its channels and folds enable greater SA for increased efficiency of its function

Question 12

function of golgi

Answer 12

• package and exports substances like proteins
• its flattened stacks of membrane lined channels increase SA
• enables vesicles to bud off (vesicle formation)
• has enzymes that help modify proteins (make it quicker)

Question 13

function of mitochondrion

Answer 13

• converts sugars (glucose) into usable form of energy - ATP

structure of mitochondria:

• most energy is made in the cristae, folds in the inner membrane
• has a greater SA due to the folds
• also contains enzymes to speed up the chemical reaction
• this enables it to efficiently carry out its functions by generating more ATP (generates 34 ATP in total)

Question 14

function of the chloroplast

Answer 14

• converts sunlight into glucose

light-dependent reaction:

• catches sunlight energy
• occurs in thylakoids
• thylakoids are in stacks called granum (increases SA making it more efficient - captures more sunlight)
• chlorophyll is in the membrane of the thylakoids (responsible for catching sunlight)

light-independent reaction:

• converts sunlight into chemical energy (glucose)
• occurs in the stroma (a cytosol like fluid)
• stroma has enzymes (biological catalysts ) that speed up chemical reactions

these two reactions occur in different locations

• the specialisation of functions enable greater efficiency
• focusses on one main function

Question 15

function of the vesicles

Answer 15

• transport substances
• lysosomes, a type of vesicle that contains digestive enzymes to break down wastes
• peroxisomes also contain many enzymes - efficiently break down toxins
• membrane-bound sacs enables them to fuse with plasma membrane

Question 16

function of the plasma membrane

Answer 16

• separates internal and external environments
• its fluid mosaic model allows certain substances to cross, and prevents others from crossing
  1. is an active and selective boundary
  2. denotes (indicates) cell identity
  3. receives external signals
  4. transports materials.

Question 17

function of channel proteins

Answer 17

channel proteins open to all molecules to diffuse into and out of the cell
substance that are usually small and charged like ions move through channel proteins (has water-filled pores for a hydrophilic environment)

Question 18

function of carrier proteins

Answer 18

• carrier proteins are responsible for the movement of larger molecules or molecules that are moving against their concentration gradient (from low concentration to high)
  
  • if movement is against the concentration gradient then ATP is required

Question 19

function of glycolipids

Answer 19

Glycolipids have a role in cell recognition so that our bodies can tell if the cell belongs to us (‘self’ cells) or are foreign cells

Question 20

function of glycoproteins

Answer 20

enables the cell to identify itself as a cell of the body

Question 21

function of cholesterol

Answer 21

• cholesterol: stabilises the membrane so it is not too fluid and not too hard

Question 22

function of receptor proteins

Answer 22

allows signals to be detected

Question 23

chemical nature of the PM

Answer 23

• the phospholipid bilayer is amphipathic (one part is water soluble, the other part is lipid-soluble)
• the phosphate heads are hydrophilic/polar (water-soluble)
• the fatty acid tails are hydrophobic or lipophilic/non-polar (fat-soluble)

Question 24

how does PM affect what substances can cross

Answer 24

• hydrophobic substances can cross the phospholipid bilayer

- hydrophilic cannot UNLESS they are small like water (the fatty acid tails’ movements allow those substances to pass

Question 25

what substances can cross through the phospholipid bilayer

Answer 25

oxygen (small + hydrophobic)
carbon dioxide (small + hydrophobic)
water (small + hydrophilic)

Question 26

what substances cross using channel/carrier proteins

Answer 26

glucose (large + hydrohphilic)
proteins (large + either)
ions - K+ NA+ (small, charged and hydrophilic)
note: charged substances are repelled by the phospholipids

Question 27

what is simple diffusion

Answer 27

• passive movement of substances from area of high concentration to area of low concentration
• when a small or hydrophobic substance moves across membrane by wiggling through phospholipids
• diffuses to equalise concentrations in the internal and external environment
• goes down concentration gradient (bc it goes from high to low concentration)
• passive - no energy required
• eg. oxygen, carbon dioxide

Question 28

facilitated diffusion

Answer 28

• same movement as simple diffusion (high to low)
• when hydrophilic or large molecules move across the plasma membrane through transmembrane proteins (proteins that cross the membrane entirely)
• down concentration gradient
• passive
• eg. sugar + ions

Question 29

active transport

Answer 29

• when molecules are ACTIVELY transported from a region of LOW concentration to a region of HIGH concentration
• carrier proteins - active transport
• goes against the concentration gradient
• eg. glucose storage

Question 30

osmosis

Answer 30

• diffusion of water (from region of high water concentration to region of low water concentration)
• diffusion of water from a region of LOW SOLUTE concentration to one of HIGH SOLUTE concentration
• occurs to maintain equilibrium on both sides of pm when the solute can’t move
• passive

eg. if you put potatoes or raisins into water, it will expand (the water is a hypotonic solution, so it has low solute concentration so water will move into the cell

Question 31

what is the fluid mosaic model

Answer 31

a model proposing that the plasma membrane and other intracellular membranes should be considered as two-dimensional fluids in which proteins are embedded

Question 32

what is an active boundary

Answer 32

a barrier that is constantly changing and responsive to the environment

Question 33

hypertonic solution and the effect

Answer 33

• when the solution has a higher solute concentration than the cell contents
• so water will move out of the cell to dilute the solution
• cell shrinks

Question 34

hypotonic solution and the effect

Answer 34

• when the solution has a lower solute concentration than the cell contents
• so water will move into the cell
• causes the cell to expand and burst if it does not have a cell wall

Question 35

isotonic solution and the effect

Answer 35

• when the solution has an equal solute concentration to that of the cell contents
• water will move in and out of the cell
• cell remains the same size