questions???

Question 1

outline evidence for the endosymbiosis theory

Answer 1

they have similar shape and size as prokaryotes
circular naked DNA like prokaryotes whilst eukaryotes have linear DNA around histone proteins
share common DNA sequences with prokaryotes
both mitochondria and chloroplasts have 70 s ribosomes whereas eukaryotes have 80s ribosomes
both divide by binary fission

Question 2

[7 marks] Explain how carbohydrates are transported from plant leaves

Answer 2

translocation/movement by mass flow;
in phloem sieve tubes;
sieve plates/pores in end walls/lack of organelles allows flow (of sap);
carbohydrates (principally) transported as sucrose;
(sucrose/glucose/sugar/carbohydrate) loaded (into phloem) by active transport;
loading/pumping in (of sugars) by companion cells;
high solute concentration generated (at the source);
water enters by osmosis (due to the high solute concentration);
hydrostatic pressure increased/high hydrostatic pressure generated;
pressure gradient causes flow (from source to sink);
leaves are a source because carbohydrates are made there;
transport to the sink where carbohydrates are used/stored;

Question 3

[3 marks] Outline how the properties of water make it an effective coolant for the body.

Answer 3

hydrogen bonds hold water molecules together
evaporation requires breaking of hydrogen bonds
water has a high heat of vaporization/high latent heat
evaporation of water cools the skin

Question 4

[5 marks] Describe how changes in weather conditions affect the transport and loss of water in plants

Answer 4

water (vapor) lost by transpiration/through stomata;
causes transport of water
faster rate of transpiration in hotter weather- more heat for evaporation
slower rate of transpiration in high humidity
more water loss when it is more windy as it carries away water vapour from the stomata
drought causes stomata to close

Question 5

[4 marks] Outline four different processes, with examples, that allow substances to pass through the plasma membrane.

Answer 5

simple diffusion from high concentration to low concentration (without the use of channels/proteins); (e.g., CO2 / O2 )
osmosis is the diffusion of water from an area of high water potential
active transport requires energy to move the molecules through a protein channel from low solute concentration to high concentration;
facilitated diffusion is passive transport through a protein channel; (e.g., glucose)

Question 5

[5 marks] Describe the structure of the DNA molecule.

Answer 5

a. two stranded/double helix ✔
b. antiparallel / strands running in opposite directions OR
one strand organized 5’ to 3’ and the other 3’ to 5’ ✔
c. sugar-phosphate backbone ✔
d. each strand formed by chains of nucleotides ✔

Question 5

[4 marks] Describe how the structure of the chloroplast is adapted to its function in photosynthesis.

Answer 5

thylakoids have a small internal volume to maximize hydrogen gradient / quickly increase concentration gradient ✔
b. many grana / thylakoids give large surface area ✔
c. (grana) contain (photosynthetic) pigments/electron carriers/ATP synthase enzymes ✔
d. (photosynthetic) pigments/chlorophyll arranged into photosystems allowing maximum absorption of light energy ✔
e. stroma has suitable pH/ enzymes of Calvin/light independent cycle ✔
f. lamellae connect/separate grana maximizing photosynthetic efficiency ✔

Question 5

3 marks] Water is the medium of life. Outline how hydrogen bonds form in water.

Answer 5

water (molecules) are polar/dipolar/have partially positive and negative poles/have δ+ and δ-;
b. attraction/bonding between positive and negative (poles);
c. hydrogen bond formed between hydrogen and oxygen; Reject if H and O in same molecule.
d. bond/attraction between different water molecules/intermolecular;