Question
Most of the surface of the Earth is covered with a wide diversity of ecosystems. Outline two general characteristics of all ecosystems.
Vascular plants can be found in a wide variety of ecosystems.
Outline active transport in phloem tissue.
Vascular plants can be found in a wide variety of ecosystems.
Explain how a plant replaces the water it loses in transpiration.
▶️Answer/Explanation
Markscheme
a. organisms/community plus the environment / biotic and abiotic «components»
b. interactions
c. ecosystems show sustainability
d. nutrients are recycled in ecosystems
e. energy flows through ecosystems
f. producers «are part of all ecosystems»
g. decomposers/saprotrophs «are part of all ecosystems»
a. active transport/pumps used to load sugars/sucrose into phloem/companion cells/sieve tubes
b. loading in sources/unloading in sinks
OR
sucrose/sugars moved from source to sink
c. active transport moves H+ out of phloem/sieve tubes «to make H+ gradient in the leaf/source»
d. H+ gradient used for co-transport of sucrose into phloem/sieve tubes/companion cells
Accept protons or hydrogen ions instead of H+ ions.
Accept the equivalent of mpc and mpd for unloading in the sink.
a. transpiration/evaporation of water causes suction/tension
b. water sucked/drawn out of xylem «in leaf»
c. water moves up in xylem
d. due to suction/tension/pulling forces
e. cohesion of water/hydrogen bonds between water molecules
f. movement from roots to leaves
g. water enters root by osmosis/due to higher solute concentration inside root
Question
Draw a labelled diagram of a eukaryotic plant cell as seen in an electron micrograph.
Outline how the energy flow through food chains limits their length.
In hot, dry conditions plants lose water rapidly due to transpiration. Explain how the structures and processes of the plant allow this water to be replaced.
▶️Answer/Explanation
Markscheme
Cell wall shown with two continuous lines to indicate the thickness
Plasma membrane/cell membrane shown as a single continuous line
Accept inner line of wall as membrane if clearly labelled.
Nuclear membrane/nucleus shown with double membrane and nuclear pores
Vacuole «membrane»/tonoplast shown as a single continuous line
Chloroplast/plastid shown with a double line to indicate the envelope and thylakoids/grana
Mitochondrion shown with double membrane/cristae
Only a small proportion/20 %/10 % «of energy» can pass from one trophic level to the next Accept named trophic levels or named stages in a food chain in place of “trophic levels”.
OR
large proportion/80 %/90 % lost between one trophic level and the next Accept if clearly shown in a diagram such as a pyramid of energy.
Energy released by respiration AND lost as heat Not just respiration or heat.
Energy losses due to uneaten parts/undigested parts/feces/egestion
Not enough energy for 4th/5th/later stages of a food chain
OR
more energy available if feeding at an earlier stage in a food chain
Evaporation of water «in leaf/mesophyll» creates tension/low pressure/negative pressure «potential»/pulling force/transpiration pull
Water drawn through cell walls/out of xylem «in leaf» by capillary action/adhesion «to cellulose»
Low pressure/tension/suction/pulling force in xylem
Hydrogen bonds make water cohesive/allow water to be pulled up under tension/allow the transpiration pull «to move water»
Xylem resists tension/low pressure/collapse with thickened/lignified walls
Water travels from the roots to the leaves in xylem
Water absorbed in roots by osmosis
Active transport of ions/solutes into roots «enabling osmosis»
Deep/wide ranging/extensive root systems/taproots/many root hairs
Thick/waxy cuticle reduces transpiration/water loss/evaporation
Small/no leaves/reduced surface area of leaves/thorns instead of leaves
Few stomata/stomata in pits/rolled leaves
Hairs on leaf surface «to reduce air flow near the leaf/reflect sunlight»
Stomata open at night/CAM physiology to reduce water loss
Question
Explain how minerals move into plants.
Outline the conditions needed for the germination of a typical seed.
Following germination of seeds, plants undergo a rapid increase in the number of cells. Describe stages in the cell cycle that result in this increase of cells.
▶️Answer/Explanation
Markscheme
Remember, up to TWO “quality of construction” marks per essay.
a. minerals bound to soil particles;
b. examples of three nutrients from: phosphate, nitrate, magnesium, iron, calcium, potassium, sodium, magnesium;
c. minerals dissolve in water;
d. mass flow causes movement of minerals with movement of water through soil;
e. minerals diffuse down a concentration gradient towards roots (as the mineral concentration next to the roots is continuously decreasing);
f. minerals enter the plant through roots;
g. by active transport / use of ATP;
h. branching of roots increases surface area for absorption of minerals;
i. root hairs increase surface area (for the absorption of minerals);
j. hypha of (mutualistic) fungi may enhance movement of selected ions into roots / increase surface area;
k. root hairs have many mitochondria to provide energy/ATP for active transport;
l. export of H+ creates electrochemical gradient / displaces ions bound to soil/clay;
m. that causes positive mineral ions to diffuse into (root) cells;
n. negative mineral ions cross membrane linked to H+ ions moving down (H+) gradient;
Remember, up to TWO “quality of construction” marks per essay.
a. water to rehydrate the seed / activate metabolic processes;
b. oxygen for aerobic respiration as seed germinates;
c. suitable temperature for enzyme activity;
d. each type of seed has specific temperature requirements / temperature requirements ensure that seeds germinate at the correct time of year;
Do not accept a simple list of factors without details.
Remember, up to TWO “quality of construction” marks per essay.
a. growth phase/G-1: synthesis of proteins/cytoplasm/organelles;
b. synthesis phase/S-phase: replication of DNA;
c. second growth phase/G-2: continued growth of cytoplasm/molecular synthesis/duplication of organelles;
d. prophase: chromosomes super-coil to prepare for mitosis / nuclear envelope disappears / spindle fibres form;
e. metaphase: chromosomes line up at equatorial/metaphase plate / spindle fibres attach to centromeres/chromosomes;
f. anaphase: chromatids move along microtubules/spindle fibres move chromatids toward opposite poles;
g. telophase: nuclear membranes form around each cluster of chromosomes;
h. cytokinesis: new plasma membrane forms between the nuclei / cell plate forms;
i. a new cell wall forms;
j. (mitosis) results in two cells with identical nuclei;
Names of phases are required to earn the mark.
Award marks for a clearly drawn correctly annotated diagram.
Question
Explain how minerals move into plants.
Outline the conditions needed for the germination of a typical seed.
Following germination of seeds, plants undergo a rapid increase in the number of cells. Describe stages in the cell cycle that result in this increase of cells.
▶️Answer/Explanation
Markscheme
Remember, up to TWO “quality of construction” marks per essay.
a. minerals bound to soil particles;
b. examples of three nutrients from: phosphate, nitrate, magnesium, iron, calcium, potassium, sodium, magnesium;
c. minerals dissolve in water;
d. mass flow causes movement of minerals with movement of water through soil;
e. minerals diffuse down a concentration gradient towards roots (as the mineral concentration next to the roots is continuously decreasing);
f. minerals enter the plant through roots;
g. by active transport / use of ATP;
h. branching of roots increases surface area for absorption of minerals;
i. root hairs increase surface area (for the absorption of minerals);
j. hypha of (mutualistic) fungi may enhance movement of selected ions into roots / increase surface area;
k. root hairs have many mitochondria to provide energy/ATP for active transport;
l. export of H+ creates electrochemical gradient / displaces ions bound to soil/clay;
m. that causes positive mineral ions to diffuse into (root) cells;
n. negative mineral ions cross membrane linked to H+ ions moving down (H+) gradient;
Remember, up to TWO “quality of construction” marks per essay.
a. water to rehydrate the seed / activate metabolic processes;
b. oxygen for aerobic respiration as seed germinates;
c. suitable temperature for enzyme activity;
d. each type of seed has specific temperature requirements / temperature requirements ensure that seeds germinate at the correct time of year;
Do not accept a simple list of factors without details.
Remember, up to TWO “quality of construction” marks per essay.
a. growth phase/G-1: synthesis of proteins/cytoplasm/organelles;
b. synthesis phase/S-phase: replication of DNA;
c. second growth phase/G-2: continued growth of cytoplasm/molecular synthesis/duplication of organelles;
d. prophase: chromosomes super-coil to prepare for mitosis / nuclear envelope disappears / spindle fibres form;
e. metaphase: chromosomes line up at equatorial/metaphase plate / spindle fibres attach to centromeres/chromosomes;
f. anaphase: chromatids move along microtubules/spindle fibres move chromatids toward opposite poles;
g. telophase: nuclear membranes form around each cluster of chromosomes;
h. cytokinesis: new plasma membrane forms between the nuclei / cell plate forms;
i. a new cell wall forms;
j. (mitosis) results in two cells with identical nuclei;
Names of phases are required to earn the mark.
Award marks for a clearly drawn correctly annotated diagram.
Question
Explain how abiotic factors affect the rate of transpiration in terrestrial plants.
Describe the importance of water to living organisms.
▶️Answer/Explanation
Markscheme
a. less transpiration/water loss as (atmospheric) humidity rises;
b. air spaces inside leaf are saturated/nearly saturated (with water vapour);
c. smaller concentration gradient with higher atmospheric humidity;
d. more transpiration/water loss as temperature rises/with more heat;
e. faster diffusion / more kinetic energy (of water molecules);
f. faster evaporation (due to more latent heat available);
g. more transpiration/water loss as wind (speed) increases;
h. humid air/water vapour blown away from the leaf;
i. increasing the concentration gradient (of water vapour);
j. more transpiration/water loss in the light;
k. light causes stomata to open / stomata closed in darkness;
l. low CO2 concentration inside leaf in bright light so stomata open wider;
Accept any of the points if clearly made on an annotated graph.
a. coolant in sweat/in transpiration;
b. water has a high heat of vaporisation / heat taken when hydrogen bonds break;
c. water is cohesive so can pulled up/so can be moved under tension in xylem;
d. water is an excellent/universal solvent/dissolves many different substances;
e. medium for transport in blood/xylem/phloem;
f. medium for metabolic reactions / (metabolic) reactions happen dissolved in water;
g. surface tension due to cohesion allows organisms to live on water surface;
h. water has high heat capacity so much energy required to change its temperature;
i. ice floats so lakes/oceans do not freeze allowing life under the ice;
j. high heat capacity so stable habitat/so temperature of water changes slowly;
k. used in chemical reactions/photosynthesis/hydrolysis in organisms;
Question
Describe four properties of water that are due to hydrogen bonding and polarity.
Describe how water is carried through a flowering plant.
Some of the water carried to the leaves of a plant is used in photosynthesis. Explain the role of water in the light-dependent reactions of photosynthesis.
▶️Answer/Explanation
Markscheme
Descriptions of properties expected not lists of properties.
hydrogen bonding:
a. high specific heat capacity requiring large amounts of energy to break the H-bonds/to raise the temperature;
b. boiling point is high/100°C as H-bonds must be broken to change from liquid to gas;
c. cooling effect of evaporation due to H-bonds taking energy from liquid water to break / high latent heat of evaporation;
d. water molecules on surface resistant to forces because of surface tension;
e. water is most dense at 4°C due to more regular hydrogen bonding;
polarity:
f. water molecules stick together through cohesion; (full idea required)
g. water molecules stick to other polar molecules through adhesion; (full idea required)
h. good solvent of polar organic molecules
a. active transport of solutes from soil into roots;
b. draws water by osmosis
c. root hairs provide a large surface area for water uptake;
d. carried through xylem vessels;
e. transpiration is the loss of water (vapour) from leaves and stems / stomata;
f. (transpiration) creates suction/pull/negative pressure;
g. cellulose wall with rings of lignin give strength to resist (low) pressure;
h. water pulled up due to capillary action/cohesion/adhesion;
i. continuous column of molecules/transpiration stream;
a. water only plays a role in non-cyclic photophosphorylation;
b. chlorophyll absorbs light/photons and activates electrons of photosystem II;
c. excited/active electrons of photosystem II are passed to carriers;
d. photolysis is the splitting of water;
e. produces O2 and H+/proton and electrons;
f. O2 released (as waste);
g. electrons (from water) replace lost electrons in photosystem II;
h. electrons from photosystem II pass (through carriers) to photosystem I;
i. electrons from photosystem I pass to NADP+ (in stroma);
j. NADP+ accepts H+/proton (from water) to form NADPH;
k. electron flow causes protons pumped across thylakoid membranes/into the thylakoid space;
l. creating a proton concentration gradient;
m. chemiosmosis couples electron transport to ATP synthesis;
n. protons pass through ATP synthase/synthetase;
o. NADPH/H+/proton is passed to the light-independent reactions (to fix carbon);
Question
The diagram shows a nephron from a mammal.
(a) Identify:
(i) structure X [1]
(ii) structure Y. [1]
(b) State the region of the kidney in which the loop of Henle is situated. [1]
(c) Explain the role of the hormone ADH in osmoregulation. [2]
(d) Outline two adaptations for water conservation in leaves of desert plants. [2]
▶️Answer/Explanation
a i proximal convoluted tubule/PCT;
a ii glomerulus/Bowman’s capsule;
b medulla;
c a. ADH secreted if blood is hypertonic/solute concentration too high/water content too low/dehydrated;
b. aquaporins open/more aquaporins in (plasma membranes of cells in DCT/collecting duct) with ADH;
c. DCT/collecting duct becomes more permeable to water/reabsorbs more water (from filtrate);
d Mark the first two answers only (thick) wax layer/cuticle; hairs on leaves/rolled leaves; sunken stomata/stomata in pits/stomata opening at night/CAM physiology; (leaves reduced to) spines/needles/no/few/small leaves/low surface area (to volume ratio) of leaves; thick stems/water storage tissue/vertical stems (to avoid most intense sunlight);