CHAPTER 16
EXTENDING YOUR IDEAS
1. a. Since this plant is a pioneer species, it will soon be supplanted by true rainforest species. Thus its survival depends upon dispersal to new gaps in the rainforest.
b. The longer the seeds stay in the gut of the bird, the lower the germination rate. The stomach acids probably cause abrasion of the seed coat. Too much abrasion might damage the seed but a low level of abrasion probably aids water absorption which would stimulate germination. Since the juice of the fruit has a laxative effect, which increases peristaltic movement of the gut, the seeds only remain in the gut for a short time.
2. a. diagram a 1. receptacle diagram b 1. anther
2. ovule 2. filament
3. filament 3. ovule
4. anther 4. stigma
5. stigma 5. style
6. petal
7. style
8. sepal
9. ovary
10. nectary
b. Both hermaphrodite; bipartite ovary.
c. a has petals and sepals, b only has a single ‘sepal’.
a has a single stigma while b has multiple stigmas.
a has one style and b has a 2 styles each leading from several stigmas.
d. While both flowers are hermaphrodite and have a full compliment of carpels and stamen, their overall structure is different, reflecting different modes of pollination. The nectary present in a is absent in b. The stamen and carpel is below the level of the petals in a. On the other hand, b does not have any petals and the reproductive structures are exposed to the air. The role of the stigma is in reception of the pollen. The stigma in a is single and large, whereas there are multiple ‘fluffy’ stigmas in b. Etc.
e. a. Insect pollinated – attracted to nectary at base of the ovary.
b. Wind pollinated – fluffy stigmas to catch the pollen in the air.
3. a. Thrum-eyed pollen is too large to fit into the grooves of the thrum-eyed stigma but can fit into those of the pin-eyed flower. The anthers of the pin-eyed flower are below the stigma surface, preventing the pollen falling onto it and encouraging insect pollination and thus transfer to the thrum-eyed form.
b. Remove the anthers of the flowers to be pollinated to ensure no self-pollination.
c. There may be chemical inhibition to self-pollen by the stigma.
d. Chemical and structural inhibition of self-pollination is incompletely developed in pin-eyed primula plants.
4. If only a small amount of pollen is released when bee visits are regular, it is unlikely that the bee will dislodge any of the pollen and so increases the chance of pollination. If bee visits are infrequent, the higher release of pollen ensures that at least some transfer of pollen will occur.
5. The production of pink, nectar-free flowers ensures that bees will visit them for their pollen, which will be transferred to another flower by the bee or cause pollen to dislodge onto a flower below. The presence of blue, nectar-rich flowers on the same plants suggests an adaptation to the ‘theft’ of nectar by the bees. As the bees hover and chew a hole in the base of these flowers, some of the pollen previously collected from pink flowers is likely to dislodge from their legs and fall on the stigma of flowers below them. The frequency of the wing beats or buzzing might also act as stimulus for release of pollen from the anthers which may then drop onto the stigmas of nearby flowers. The nectar-rich blue flowers, therefore, might act as a lure to attract the bees and so provide a second chance for pollination.
Hypothesis: The production of nectar-rich blue flowers by the panicled bluebell in addition to pollen-rich pink flowers, acts as an additional attractant to ensure maximum pollination.
6. a. 1 metre above the ground.
b. 1 metre above the ground.
Growth of the tree trunk is from the apex.
7. The lack of buoyancy of air and the force of gravity would limit the height to which the plant could grow. Without the skeletal support provided by the wood formed as a result of secondary growth, the plant would start to droop and bend over as it increased in height, as would side branches. This could lead to breakage of the stems and would limit flower and growth development. Thus plants which do not display secondary growth tend to be low and spreading, mechanical support being limited to turgor pressure.
8. a.
Time (days) / Height (mm) / Growth rate (mm/day)0 / 0 / 0
10 / 20 / 2
20 / 80 / 6
30 / 280 / 20
40 / 760 / 48
50 / 1240 / 48
60 / 1660 / 42
70 / 1960 / 30
80 / 2000 / 2
90 / 2000 / 0
b. 50
40
growth rate
(mm/day) 30
20
10
0
0 10 20 30 40 50 60 70 80 90
days from planting
c. Greatest increase in height occurs between days 30 and 50, whilst the period of least increase occurs between days 80 and 90.
d. There would be little or no increase in height. It is an annual flowering plant and thus does not have secondary growth. This is a limiting factor in height increase.