B2.1 - supplying the cell

Question 1

Is diffusion a passive/active process

Answer 1

= Passive process, no energy is transferred

Question 2

Factors to increase rate of diffusion:

Answer 2

• decrease distance the particles need to move
• increase concentration gradient
• increase surface area

Question 3

Describe how diffusion links to cells:

Answer 3

Diffusion is one process by which particles enter/leave cells
- pass through cell membrane from region of high conc to region of low conc

Question 4

Describe examples of diffusion into cells

Answer 4

All cells need glucose & oxygen for respiration

• Blood transports these around your body
• Then substances diffuse into cells that need them

Question 5

Why might diffusion occur out of cells? Describe an example of diffusion out of cells:

Answer 5

Some chemical reactions that happen inside cells make waste products, can be toxic
- CO2 is poisonous at high levels, diffuses out of respiring cells

Question 6

Osmosis:

Answer 6

= diffusion of water molecules across a selectively permeable membrane (into/out of cells)

Question 7

Water potential:

Answer 7

= conc of free water molecules

(when solute dissolves in water, water molecules cluster around solute molecules, leaves fewer water molecules free to diffuse to other areas)

Question 8

What has the highest water potential?

Answer 8

= pure water

Question 9

What is the relationship between concentration and water potential?

Answer 9

More concentrated solution = lower water potential

Question 10

Explain osmosis in terms of water potential:

Answer 10

= movement of water molecules from a high water potential to a low water potential

Greater difference in water potential = greater rate of osmosis

Question 11

Osmosis in PLANT cells:

Answer 11

• surrounding solution less concentrated (higher water potential)
  = takes up water by osmosis, turgor pressure (pressure in cell) increases, becomes firms/turgid
• surrounding solution more concentrated (lower water potential)
  = loses water by osmosis, turgor pressure falls, becomes flaccid(soft), eventually cell contents collapse away from cell wall = plasmolysed cell

Question 12

Osmosis in ANIMAL cells:

Answer 12

• surrounding solution less concentrated (higher water potential)
  = takes up water by osmosis, swells/may burst = lysis
• surrounding solution more concentrated (lower water potential)
  = loses water by osmosis, becomes crenated(crinkles)

Question 13

Active transport:

Answer 13

= allows cells to move substances from an area of low conc to an area of high conc, against concentration gradient (energy must be transferred from energy store)

Question 14

3 key features of active transport:

Answer 14

• particles are transported (pumped) against a concentration gradient
• ATP required (from respiration)
• process makes use of carrier proteins in cell membrane

Question 15

What do cells that carry out lots of active transport contain and why?

Answer 15

= lots of mitochondria

- can respire rapidly to produce large quantities of ATP

Question 16

What does the rate of active transport depend on?

Answer 16

= rate of respiration to produce required ATP

Question 17

Carrier proteins:

Answer 17

= special proteins that span width of cell membrane,

Question 18

Describe how carrier proteins carry out active transport:

Answer 18

• particular molecules cell requires binds to specific carrier protein
• energy transferred from ATP to protein so it can change shape/rotate
• carrier protein transport molecule into cell
• rotates back again (using more energy/ATP)

Question 19

Example of active transport in digestion:

Answer 19

• in small intestine, carbohydrates broken down into glucose
• glucose is actively transported into bloodstream through the villi
• blood takes glucose to wherever it’s needed in body

Question 20

Example of active transport in nerve cells:

Answer 20

• carrier protein actively pumps sodium ions out of cell as potassium ions pumped back in
• sodium potassium pump plays important role in creating nerve impulses

Question 21

Examples of active transport in plants:

Answer 21

• to take minerals in from soil
• plants need nitrate ions to make proteins for growth
• normally lower conc in soil water surrounding roots than in plant
• plant root hair cells use active transport to move nitrate ions across cell membrane into root cell

Question 22

Mitosis

Answer 22

= process by which body cells divide

To replace worn out cells, repair damaged tissue, enable organism to increase in size

Question 23

What does each cell divide into?

Answer 23

• each cell divides to produce two identical daughter cells = clones
• increases number of cells in multicellular organism

Question 24

What is the cell cycle, name the 4 stages:

Answer 24

= process of cell growth & division (cell cycle = daughter cells continue)

• DNA replication
• movement of chromosomes
• cytokinesis
• growth of daughter cell

Question 25

DNA replication:

Answer 25

- DNA molecules unzips forming 2 separate strands - DNA bases 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) - forms DNA base pairs - when whole strand complete, there are 2 identical molecules of DNA - DNA molecules zip back up

Question 26

Movement of chromosomes:

Answer 26

- chromosomes line up across centre of cell - the 2 identical copies of each chromosome separate & move to opposite ends of cell - each end now contains full set of identical chromosomes - 2 new nuclei then form

Question 27

Cytokinesis:

Answer 27

- cell membrane pinches inwards to separate & enclose the 2 new nuclei - pinches off to split original cell into 2 new, genetically identical daughter cells

Question 28

Example of where mitosis occurs rapidly:

Answer 28

- humans constantly lose cells from surface of skin - mitosis occurs constantly to replace these cells (Approx 300 million body cells die & are replaces evert minute)

Question 29

Cell differentiation:

Answer 29

= cells becomes specialised to perform a particular job, during the development of a multicellular organism

Question 30

Examples of cells that become so specialised they can only perform one function in the body:

Answer 30

- sperm cell - fat cell - red blood cell - ciliated cell - palisade cell

Question 31

Sperm cell differentiation & adaptations:

Answer 31

= specialised to transfer to genetic material from male to ovum(egg) - flagellum, propels sperm to ovum - lots of mitchondria, respiration reactions transfer energy from chemical stores to move flagellum - acrosome, stores digestive enzymes which break down outer layers of ovum to allow sperm to transfer its genetic material

Question 32

Fat cell differentiation & adaptations:

Answer 32

= specialised to store fat - small layer of cytoplasm surrounding a fat reservoir, so can expand up to 1000 its original size as they fill with fat

Question 33

Red blood cell differentiation & adaptations:

Answer 33

= specialised to transport oxygen around body - biconcave discs, biconcave shape = increases surface area to volume ration, increases diffusion of oxygen into cell, carbon dioxide out of cell - packed full of haemoglobin, protein bings to oxygen to form oxyhaemoglobin(bright red) - no uncles, more space for haemoglobin molecules

Question 34

Ciliated cells differentiation & adaptations:

Answer 34

= specialised to sweep mucus, produced by goblet cells, away from lungs to back of throat, mucus then swallowed, bacteria killed in stomach - cilia (tiny hairs) on top of cell sweeps mucus

Question 35

Palisade cells differentiation & adaptations:

Answer 35

= specialised for carrying out photosynthesis - found near surface of leaf, closer to sunlight - packed full of chloroplast, absorbs more sunlight & converts to more energy - regular shape, to allow close packing within leaf, maximising absorption of sunlight

Question 36

Stem cells:

Answer 36

= undifferentiated cells Can develop into any type of specialised cells, form all types of tissues/organs (divide by mitosis, forming cells which develop into specialised cells)

Question 37

Embryonic stem cells:

Answer 37

- found in embryos - divide by mitosis to produce all cells needed to make an organism - have the ability to differentiate into all cell types

Question 38

Adult stem cells:

Answer 38

- found in various body tissues (brain, bone marrow, skin, liver) - ability to differentiate into some different types for cell, but not all

Question 39

What do blood stem cells (in bone marrow) differentiate into:

Answer 39

- red blood cells - white blood cells - platelets

Question 40

What are the main purpose of adult stem cells:

Answer 40

= act as a repair mechanism for the Boyd - once animal fully grown, adult stem cells remain in non-dividing state for years - if activated by disease/tissue injury, cells start to divide - generates many cells, can be used to repair damage

Question 41

Where are stem cells found in plants, why?

Answer 41

= meristems (shoot/root tips) = particular part of plant that continues to grow throughout their life

Question 42

How are stem cells in plants different to normal plant cells:

Answer 42

- very thin walls - small vacuoles - no chloroplasts

Question 43

why can’t differentiated plant cells divide?

Answer 43

= cell walls are thick & rigid