Question
The Santa Cruz tarplant, Holocarpha macradenia, is a tall annual plant that grows only in the coastal grasslands in California. An annual plant is one that grows, flowers, produces seeds and dies in less than one year.
The tarplant used to be widely spread in California, but there are now only nine natural populations. It is listed as an endangered species.
(a) (i) Suggest two reasons why the tarplant has become endangered.[2]
(ii) State three reasons why it is important to conserve species.[3]
1
2
3
(b) Tarplant seeds can survive in the soil for several years. Dormant seeds can be encouraged to germinate by scraping the soil, which exposes them to light. This stimulates the production of gibberellin in these seeds, which brings about germination.
Explain how gibberellin brings about germination in seeds.[4]
(c) The long-term survival of tarplant seeds in the soil provides a store of seeds that can help to ensure the future survival of the tarplant.
Little is known about the survival of tarplant seeds in the soil, or what percentage of these seeds is able to germinate. Researchers therefore used computer models to predict how these factors could affect the likelihood that the tarplant might become extinct.
In their models they used:
- high or low survival values of tarplant seeds in the soil
- different germination percentages of tarplant seeds.
The predictions of the models are shown in Fig. 4.1.
(i) With reference to Fig. 4.1, describe the effect of each of the following on the risk of extinction of the tarplant:[3]
high compared to low survival of the tarplant seeds
different germination percentages of the tarplant seeds.
(ii) With reference to Fig. 4.1, discuss whether scraping the soil should be recommended as part of the management strategy to attempt to conserve the tarplant.[3] [Total: 15]
Answer/Explanation
Ans:
4 (a) (i) 1 habitat loss / urbanisation/roads /agriculture ; R deforestation
2 human damage (to plants) ; e.g. trampling / camping/ picking
3 climate change ; e.g. drought/ storms
4 soil erosion ;
5 loss of pollinators ;
6 use of herbicides ;
7 competition with/ eaten by, introduced species ;
8 pollution ;
(ii) 1 to maintain biodiversity ;
2 to maintain, food chains / food webs / stability of ecosystems ;
3 to maintain, genetic diversity / genetic variation/ gene pool ;
4 resources (for humans) ; e.g. biofuel/ food/medicines /wood
5 aesthetic reasons /(eco)tourism ;
6 to maintain, nutrient cycle/ soil structure/ climate stability ;
7 idea of ethical duty ;
(b) 1 gibberellin moves (from embryo) to aleurone layer ;
2 gene, switched on/ transcribed/used to make mRNA ;
3 amylase produced ; I released/ stimulated
4 (amylase), hydrolyses / digests, starch to maltose ; I breaks down/ converts / glucose
5 for, respiration/ATP/ energy ;
6 for, growth/development/ cell division/mitosis, in embryo ;
7 AVP ; e.g. role of, DELLA/PIF
(c) (i) survival:
1 less risk of extinction (for high seed survival compared with low survival) ;
germination percentage:
for low survival:
2 as % germination increases, risk of extinction decreases ;
for high survival:
3 as % germination increases risk of extinction decreases until,
30–36 % germination, then risk of extinction increases ;
4 use of paired figures ; e.g. quote % germination and risk of extinction for each of:
high v low [mp1]
2 points on low survival line [mp2]
2 points on high survival line [mp3]
allow ± one grid square for figures
(ii) yes
1 (scraping) increases germination ;
2 more germination lowers risk of extinction ; ora
3 if seeds don’t survive long/ for low survival value seeds, scraping is good ;
no
4 if seeds do survive long-term/ for high survival value seeds, a store of seeds remains in soil ;
5 (avoid risk of) all germinating at once and perhaps all dying ;
Question
Bread wheat, Triticum aestivum, is a hexaploid that has developed from diploid wild grasses.
(a) Outline the process by which T. aestivum has developed from wild grasses.[4]
(b) Wheat seeds begin to germinate when they are in warm conditions and can take up water.
Fig. 4.1 shows a germinating wheat seedling.
The endosperm contains starch stores. There are also small quantities of sucrose stored in the aleurone layer.
Water uptake stimulates the production of a plant growth regulator in the seed, which in turn activates the synthesis of enzymes in the aleurone layer. These enzymes hydrolyse starch to maltose and glucose.
Name the plant growth regulator involved in the activation of the synthesis of the enzymes.[1]
(c) An investigation was carried out into the role of a gene, TaSUT1, which codes for a sucrose transporter protein, in the germination of wheat seeds.
- Wheat seeds were germinated and left to grow for 3, 7 or 10 days.
- Samples of tissues from the roots, seeds and shoots of the seedlings were tested for the presence of mRNA transcribed from TaSUT1.
- The extracted mRNA was mixed with a probe, and then placed on agarose gel across which a voltage was applied.
The results are shown in Fig. 4.2.
(i) Suggest why the researchers looked for mRNA transcribed from the TaSUT1 gene, rather than for the gene itself.[2]
(ii) Explain what the results in Fig. 4.2 indicate about the sequence of activity of TaSUT1, from day 3 to day 10, in the root, seed and shoot of a seedling.[2]
(d) TaSUT1 codes for the sucrose transporter protein, SUT. This protein transports only sucrose.
To investigate where this protein was present in a germinating wheat seedling, a fluorescent antibody for SUT was added to sections of tissues from the seedling.
(i) Suggest how this enabled the researchers to determine the areas where SUT was located.[2]
(ii) Immediately after germination began, SUT was found in the membranes of cells in the aleurone layer. It was also determined that the most common sugar in the endosperm in the first hours after germination was sucrose.
Explain how these results support the hypothesis that the first source of sugar for the embryo during germination is sucrose from the aleurone layer and not sugars produced by the hydrolysis of starch.[2]
(iii) SUT appeared in the developing phloem tissue within three days of the start of germination.
Outline how sucrose is transported in phloem.[3] [Total: 16]
Answer/Explanation
Ans:
4 (a) 1 cross between, two wild grasses / einkorn and goat grass ;
2 hybrid/ offspring, sterile ;
3 chromosome doubling ;
4 due to nondisjunction ;
5 formation of, tetraploid/ 4n/ polyploid ;
6 diploid/ 2n, gametes now formed ;
7 new cross with a, diploid/ 2n, wild grass ;
8 hybrid/ offspring, sterile ;
9 hybrid/ offspring, triploid/ 3n ;
10 chromosome doubling ;
allow mp2 or mp8 not both
allow mp3 or mp10 not both
(b) gibberellin/ gibberellic acid ;
(c) (i) 1 gene would be present in every cell ;
2 (when gene expressed) mRNA is in large amounts ;
3 difficult to, isolate/ identify /extract, gene ;ora for mRNA
(ii) (from day 3 to day 10)
1 activity /SUT production, in seed decreases
because darkness (of bands) decreases ;
2 activity /SUT production, in shoot increases
because darkness (of bands) increases ;
3 activity /SUT production, remains constant in root
because darkness (of bands) stays the same;
(d) (i) 1 (fluorescent) antibody binds with, SUT/ the sucrose transporter protein ;
2 view/ photograph, tissues / sections, with a microscope ;
3 fluorescent areas indicate presence of SUT ;
(ii) 1 presence of SUT in aleurone layer indicates sucrose moves (from aleurone layer to endosperm) ;
2 hydrolysis of starch, produces glucose or maltose/ does not produce sucrose ;
(iii) 1 active transport/pumping, of hydrogen ions out of companion cells ;
2 (at source sucrose) loaded, by cotransport/with hydrogen ions (into companion cells) ;
3 water moves into, companion cell/ sieve tube (element) ;
4 by osmosis ;
5 idea of a hydrostatic pressure gradient ;
6 mass flow ;
Question
(a) When a dormant seed absorbs water it will start to germinate and its rate of respiration will increase.
Name the plant growth regulator involved in the initiation of germination of seeds.[1]
(b) A respirometer can be used to measure the rate of respiration of germinating seeds.
Fig. 8.1 shows a respirometer.
(i) State the role of potassium hydroxide solution in the use of a respirometer.[1]
(ii) As respiration takes place, oxygen is used by the seeds and the coloured liquid moves down the tube.
Describe the role of oxygen in aerobic respiration.[3]
(c) Respirometers, as shown in Fig. 8.1, were used to investigate the effect of temperature on the rate of respiration of germinating pea seeds.
Four respirometers, A, B, C and D were set up:
- A and B in a water-bath maintained at 10°C.
- C and D in a water-bath maintained at 25°C.
- A and C each contained 30 germinating pea seeds.
- B and D each contained glass beads with a total volume equivalent to 30 pea seeds.
- The respirometers were left in the water-baths for 10 minutes.
- In each respirometer the position of the coloured liquid in the graduated tube was then marked (time 0 minutes).
- After 5 minutes the distance moved by the coloured liquid was measured.
- The volume of oxygen taken up was calculated for each respirometer.
- This was repeated after 10, 15 and 20 minutes.
Fig. 8.2 shows the results of the experiment.
(i) Suggest why the respirometers were left for 10 minutes before measurements were made.[1]
(ii) Suggest why respirometers B and D were used in this investigation.[2]
(iii) Calculate the rate of oxygen uptake in cm3 per minute for respirometer C between 5 and 20 minutes.
Give your answer to two significant figures.
Show your working.
answer cm3 min–1 [2]
(iv) Explain why there is an increased rate of respiration of germinating pea seeds between 10°C and 25°C.[2]
(v) Suggest why carrying out the experiment with germinating seeds at 50°C could result in a lower rate of respiration than at 25°C.[2] [Total: 14]
Answer/Explanation
Ans:
8(a) gibberellin ;
8(b)(i) absorbs carbon dioxide ;
8(b)(ii) three from
1 used in, oxidative phosphorylation /ETC ;
2 final electron acceptor ;
3 proton acceptor ;
4 forms water ;
5 allows ETC to continue ;
6 ref. to ATP produced ;
8(c)(i) equilibration/ acclimatising / adjusting ;
8(c)(ii) two from
1 act as a control ;
2 idea of control eliminates effects of variables other than, the independent variable / temperature ;
3 (changes in A and C are) due to, seeds /respiration ; ora
8(c)(iii) 0.087 ; ;
allow one mark for
\(\frac{1.7-0.4}{15}\) \(\frac{1.3}{15}\) \(\frac{1.3}{20-5}\) \(\frac{1.7-0.4}{20-5}\)
or
0.08666
8(c)(iv) at 25°C (ora for 10°C)
two from
1 increased kinetic energy ;
2 enzymes involved ;
3 idea of more ESCs ;
8(c)(v) enzymes denatured ;
detail ; e.g. change in active site (shape)/H bonds break