B1 - Cell structure and transport

Question 1

What is the equation for magnification?

Answer 1

mag = image size/actual size

Question 2

Label all 6 parts of a microscope on a diagram:

Answer 2

The microscope can also have a small pointer or scale inside the eyepiece

Question 3

What are the pros and cons of electron microscopes?

Answer 3

-higher mag/resolution to see sub-cellular structures
-can give 3D images (only scanning, not transmission)

-specimen must be dead
-expensive to operate (needs special temperature/pressure)

Question 4

Explain the functions of the 5 organelles of animal cells:

Answer 4

nucleus - controls cell functions and houses genetic info
cytoplasm - site of chemical reactions, and holds all organelles
cell membrane - controls substances entering/leaving cell
mitochondria - site of aerobic respiration
ribosome - site of protein synthesis

(nuke cyto cell mito ribo)

Question 5

What organelles do plant cells have that animal cells don’t?

Answer 5

chloroplasts - site of photosynthesis and contains chlorophyll
permanent vacuole - contains cell sap, draws water in to keep it turgid
cell wall - made of cellulose, ^strength

Question 6

Describe a eukaryotic cell:

Answer 6

plant/animal cell that have genetic material enclosed in a nucleus and divides by mitosis

Question 7

What is a prokaryotic cell? Explain how it is different to a eukaryote:

Answer 7

-a bacteria cell that has single DNA loop not enclosed in a nucleus that divides by binary fission

-can have flagella/slime capsule/extra plasmids
-cell wall has no cellulose

Much smaller in comparison to eukaryotes

Question 8

How are sperm cells specialised?

Answer 8

-tail for movement
-lots of mitochondria for aerobic repsiration
-front acrosome has digestive enzymes to break into egg
-large nucleus for chromosomes

Question 9

How are nerve cells specialised?

Answer 9

-insulated axon to transmit electrical impulses faster (myelin sheath)
-dendrites to connect to other nerve cells
-synapses to transmit impulses

Question 10

How are muscle cells specialised?

Answer 10

-mitochondria for aerobic respiration
-stores glycogen
-elongated, space to contract
-proteins that help fibres slide over each other to contract for movement

Question 11

How are root hair cells specialised?

Answer 11

-protruding root hair to ^SA for osmosis
-large PV to draw water in by osmosis
-mitochondria for AT of mineral ions

Question 12

How are xylem cells specialised?

Answer 12

-dead cells form long hollow tubes to transport water + ions up plant
-lignin spiral helps withstand pressure of water
-cell walls line up on outside of the vessel to strengthen stem

Remember that xylem has dead cells, because it starts with an x

Question 13

How are phloem cells specialised?

Answer 13

-their cell walls form sieve plates to allow for 2-way movement of dissolved sugars (food/glucose) from photosynthesis

-companion cells have mitochondria for AT

Question 14

What is diffusion?

Answer 14

the spreading out of particles of a substance in solution (or gas particles), resulting in a net movement from an area of higher to lower concentration

Question 15

Give 4 factors that affect the rate of diffusion:

Answer 15

-concentration gradient
-temperature
-surface area of membrane (eg CM)
-diffusion path distance (for things like capillaries)

(CTSD)

Question 16

Why does a unicellular organism not need complex structures to perform gas exchange?

Answer 16

-high SA:V
-shorter diffusion path
-diffusion via CM is good enough

Question 17

Unicellular organisms can just use diffusion to exchange materials with the environment, but larger organisms can’t because…

Answer 17

-lower SA:V
-gases/food can’t reach every cell inside the organism
-metabolic waste can’t be removed fast enough

Question 18

How do multicellular organisms make their substance exchange surface more effective?

Answer 18

-^SA
-make the membrane thinner
-ventilate the CG (eg with blood or breathing)

Question 19

What is osmosis?

Answer 19

net movement of water molecules from a dilute (hypo) solution to a concentrated (hyper) solution through a PPM

Question 20

Name the states that the plant cell will be in when placed in a hypo/iso/hypertonic solution:

Answer 20

hypo - turgid (may burst, too much water)
iso - flaccid (equilibrium)
hyper - plasmolyzed (v. less water)

hypo, lots of H2O

Question 21

What is active transport and where is it used?

Answer 21

-movement of substances against a concentration gradient, which requires energy from respiration

-plant roots absorbing mineral ions for growth
-SI absorbs sugar molecules for respiration

Always say that last point about how energy is required

Question 22

How are fish gills adapted for substance exchange?

Answer 22

-gills have stacks of filaments (^SA) which all have a rich blood supply
-water is constantly flowing over them and is pumped by the operculum (a flap)

Question 23

RP1 - Describe the steps needed to observe a section of plant/animal cells:

Answer 23

-mount slide with a drop of water, then sample, then 2 drops of iodine solution to stain

-lower the cover slip 1 side at a time using mounting needles (ensuring there are no bubbles), then put slide on stage

-turn on lamp, look through eyepiece on lowest mag. then use coarse focus to focus

-repeat with the higher magnifications using fine focus until at the highest

Question 24

RP1 - Why should a thin layer of stained cells be used? How does the stain achieve its purpose?

Answer 24

thin -light can pass through (observe its subcellular structures)

stained - adds further contrast (iodine reacts with the starch and turns blue-black)

Usually stained with iodine solution

Question 25

RP3 - How can you investigate osmosis using plant tissue and sugar solutions?

Answer 25

-use cork borer to cut 5 potato cylinders of equal size (trim using ruler + knife), record mass of each

-label at least 5 test tubes with the concentration of sugar solutions inside them (1M, 0.75M, 0.5M, 0.25M, 0M) and add a potato cylinder to each to leave overnight

-remove cylinders, blot dry with tissues, measure mass, calculate %change for each, plot graph of %change vs concentration

Question 26

RP3 - Suggest 4 sources of error in the experiment testing osmosis with different sugar solutions:

Answer 26

-concentration of solutions
-drying of potato sections
-accuracy of balance
-evaporation from sugar solution test tubes