B2.1 Supplying the cell Flashcards
1
Q
Explain how substances are transported into and out of cells through diffusion
A
- net (overall) movement of particles from a region of high concentration to low concentration
- move down a concentration gradient
- diffusion continues until concentration of particles is same everywhere (0 con gradient)
- passive process (no energy required - it’s as of ordinary motion of particles)
2
Q
State which factors affect the rate of diffusion and explain why
(Include examples)
A
Distance
- decrease distance that particles need to move - it takes less time to travel a shorter distance
- (blood capillaries are only one cell thick, increasing rate of diffusion of gases into + out of bloodstream)
Concentration grad
- increase it - the steeper the concentration grad, the greater the net movement of particles
- (plants use CO2 for photosynthesis, so the CO2 levels inside the plant cells drops, increasing diffusion rate of CO2 into cells)
Surface Area
- Increase SA, allowing more space for diffusion, so more particles can move in a period of time
- (small intestine wall is highly folded, increasing SA in contact with bloodstream, which increases diffusion rate of molecules produced in digestion - amino acids + glucose)
3
Q
State an example of diffusion in the body
A
- blood transports glucose + O2 around body for respiration
- glucose + O2 diffuse into cells that need them
- chemical reactions happen inside cells making waste products e.g. CO2 (poisonous/toxic at high levels) so it diffuses out of respiring cells
- particles pass through cell membrane from high to low con
4
Q
Explain how substances are transported into and out of cells through osmosis
A
- movement/diffusion of water molecules from a high water potential to a lower water potential through a selectively permeable membrane
- down a con grad
- concentration of free water molecules - water potential (the more concentrated a solution, the lower the water potential)
- the greater the difference in water potential, the greater the rate of osmosis
5
Q
Explain the effect of placing plant cells into solutions of differing water potential
A
Surrounding con (water potential) than cell contents - which type of solution -effect
Low con (high water potential)
- dilute solution
- takes up water by osmosis
- turgor pressure increases
- cell becomes firm/ turgid
Same con
- no net movement
- cell stays the same
More con (low water potential)
- concentration solution
- loses water by osmosis
- turgor pressure falls
- cell becomes flaccid (soft) and later cell contents collapse away from cell
- called plasmolysed cell
6
Q
Explain the effect of placing animal cells into solutions of differing water potential
A
Surrounding con (water potential) than cell contents - which type of solution -effect
Low con (high water potential)
- dilute solution
- takes up water, swells and may burst
- called lysis
Same con
- no net movement
- cell stays the same
More con (Low water potential)
- concentrated solution
- loses water by osmosis
- becomes crenated (crinkled)
7
Q
State the equation for percentage change
A
((N - O) / O) x 100
8
Q
Explain how substances are transported into and out of cells through active transport
A
- low con to high con - move against con grad therefore energy must be transferred from an energy store
3 key features: - particles transported (pumped) against con grad
- ATP required by respiration
- makes use of carrier proteins in cell membranes
- need lots of mitochondria to retire rapidly and produce ATP required for active transport - rate of active transport occurring depends on rate of respiration
Process:
- carrier proteins span (stretch across) the width of the cell membrane
- a particular molecule that the cell required binds to a specific carrier protein
- energy is transferred from an energy store to the protein so that it can change shape or rotate
- the carrier protein transports the molecule into cell
9
Q
Describe some examples of active transport
A
Digestion:
- times when glucose con in intestine is lower than in bloodstream
- glucose is actively transported into bloodstream through the villi from the small intestine (where carbs are broken down into glucose)
- blood takes glucose to wherever needed
Nerve cells
- carrier protein actively pumps sodium ions into cell
- at the same time potassium ions are pumped back in
- sodium potassium pump plays important role in creating nerve impulses
Plants:
- plants need nitrate ions to make proteins for growth
- normally a lower con of nitrate ions in the soil water surrounding the roots than in the plant
- active transport used to more these ions across cell membrane into root cell
10
Q
State the purpose of mitosis ( + 4 stages of cell cycle)
A
- process by which body cells divide to produce 2 genetically identical daughter cells
- increases no. of cells in a multicellular organism
- in some parts of plants and animals, mitosis occurs rapidly all the time
- 4 stages of cell growth + division (cell cycle):
- DNA replication
- movement of chromosomes
- cytokinesis
- growth of daughter cell
11
Q
Describe the process of DNA replication in mitosis
A
- involves copying its chromosomes so that each new cell produced will include a complete set of genetic material
- the chromosome’s DNA (1 strand) is replicated
- DNA molecule ‘unzips’ forming 2 separate strands
- DNA based on each strand are exposed
- free nucleotides in nucleus line up against each of the strands following rule of complementary base pairing (A-T, C-G)
- this forms DNA base pairs
- when whole strand is complete, there are 2 identical molecules of DNA
12
Q
Describe the process of mitosis (Movement of chromosomes, cytokinesis + growth of daughter cell)
A
Movement of chromosomes
- chromosomes line up across centre of cell
- 2 identical copies of each chromosome formed during DNA replication separate and move to opposite ends of cell
- each end now contains a full set of identical chromosomes
- 2 new nuclei then form
Cytokinesis
- cell membrane pinches inwards time separate and enclose the 2 new nuclei, then pinches off to split original cell into 2 new genetically identical daughter cells
- each daughter cell then grows independently
- following growth of daughter cells, they begin replicating their DNA - the cell cycle continues
13
Q
Explain the importance of cell differentiation
A
- during development of a multicellular organism, cells differentiate (become specialised to perform a particular job)
- when it becomes specialised, its structure changes so that it’s better adapted to perform its function
- this makes entire organism more efficient, as life processes are carried out more effectively
- some cells become so specialised that they only perform 1 function within the body
14
Q
Describe the adaptations of sperm cells
A
- specialised to transfer genetic material from the male to the ovum
- flagellum (tail) - whips from side to side to propel sperm to ovum
- lots of mitochondria - respiration occurs, and the reactions transfer energy from chemicals stores so that the flagellum can move
- acrosome - stores digestive enzymes, which break down outer layers of ovum to allow sperm to transfer + incorporate its genetic material
15
Q
Describe the adaptations of fat cells
A
- specialised to store fat
- can be used as store of energy, enabling animal to survive when food is short
- fat cells also provide animals with insulation + are used to form a protective layer around some organs e.g. the heart
- but, too much fat in humans is dangerous to health
- adapted by having a small layer of cytoplasm surrounding a fat reservoir
- they can expand up to 1000 x their original size as they fill with fat
