|Answers to review questions – chapter 36
1. Make a list of the major problems of living on land compared with living in water. What adaptations to living on land are associated with the gametophyte generation and the sporophyte generation in the life cycle of plants? (pp. 869–873)
The land environment is significantly different to an aquatic environment in that water is a limiting commodity. Water supports aquatic plants, while land plants require extra structural support before they can increase in size. There are two major differences affecting the metabolism of land and aquatic plants: water balance and gas exchange. To avoid desiccation, land plants require protective layers, both on the plant body in general (development of a waterproof cuticle), and on spores and pollen. The requirement of free water for sperm motility in sexual reproduction in bryophytes explains why most bryophytes are restricted to moist conditions. Adaptations to this mode of reproduction include the development of paraphyses to trap water around the reproductive organs. As the land plants evolved, the gametophyte generation became reduced and more physically protected from desiccation.
2. Of the following phyla of living plants, which have vascular tissue: Hepatophyta, Bryophyta, Psilophyta, Filicophyta, Coniferophyta, Magnoliophyta? Which of these phyla are ferns? Which of these phyla are liverworts? (pp. 873–897)
Psilophyta, Filicophyta, Coniferophyta and Magnoliophyta are all vascular phyla, bearing xylem and phloem tissues. Filicophyta are ferns (Psilophyta belong to a loose grouping of vascular plants called the ‘fern allies’, but they are not true ferns) and Hepatophyta are liverworts.
3. What are antheridia and archegonia and on what stage of the plant life cycle do they develop? (p. 873)
Antheridia—Male gametangium (sex organ) producing sperm (or male haploid nuclei); antheridia are unicellular in algae and fungi and multicellular in plants (lower vascular plants). The antheridia develop on the male gametophyte.
Archegonia—Multicellular, female gametangium (sex organ) producing egg cells; in all plants except flowering plants. Archegonia develop on the female gametophyte.
4. Draw and label a sporophyte of a moss. (p. 878)
Refer to Figure 36.16.
5. What is meant by ‘homosporous’ and ‘heterosporous’ plant life cycles? Is a pine tree homosporous or heterosporous? (p. 873, Table 36.2)
Homosporous means the production of one type of spore, while heterosporous means the production of two types of spores, i.e. male and female. Pine trees are heterosporous, with microspores giving rise to pollen, and megaspores giving rise to ovules.
6. What is a megaspore and a microspore, and what do each of them develop into? (p. 873)
Megaspores and microspores are the two types of spores produced by heterosporous plants. Megaspores germinate into female gametophytes, which in turn produce archegonia, containing egg cells. Microspores develop into male gametophytes, producing antheridia containing sperm.
7. (a) What is a seed and from what structure(s) does it develop? (p. 886)
A seed is a fertilised ovule (enclosing the female gametophyte), which contains the embryonic sporophyte plant.
(b) In what ways is the seed an important advantage to plants living on land? (p. 886)
Seeds are an important development of land plants, providing an additional protective layer for the embryo, enabling the embryo to survive until conditions become optimal for germination and growth. This permits the reduction and retention of the gametophyte stage within the sporophyte.
8. Name the parts of a flower and state a function for each. (p. 895)
There are generally four whorls of flower parts, surrounding a central axis: in the centre are the carpels, each consisting of a stigma, style and ovary, which contains the ovules. Surrounding this are the stamens supporting the anthers, which bear the pollen sacs. These are surrounded by the corolla, a ring of usually colourful, leaf-like structures, and then a whorl of leaf-like sepals, which protect the inner layers during early development.
9. It has been stated in this book that carpels are the most distinctive reproductive organs of flowering plants (angiosperms). What is a carpel and what advantages do carpels give to flowering plants? (p. 896)
The carpel is a protective covering which surrounds the ovary. As the ovary develops into seeds, the carpel becomes the fruit. Carpels provide protection to the ovary as it develops into seeds. Additionally, the development of the carpel into a fruit has the advantage of attracting animals for pollination and fruit and seed dispersal.
Fruits are classified as simple fruits (including berries, pomes, drupes, follicles, legumes and capsules), aggregate fruits or multiple fruits. Using these terms, classify the following fruits: strawberry, tomato, apple, eucalypt ‘gumnut’, Acacia pod, pineapple, plum and grape. (p. 901)
1. Strawberries are aggregate fruits, with several small achenes on a central fleshy receptacle.
2. Tomatoes are berries, fleshy fruits with many seeds enveloped within a fleshy mesocarp, surrounded by a clearly defined exocarp.
3. Apples are pomes, with the core being the true fruit, derived from the ovary, and the flesh derived from the receptacle, sepals and petal bases.
4. Eucalyptus gumnuts are capsules, a woody structure consisting of several valves that open as they are heated, for example by fire.
5. Acacia pods are legumes, pods of seeds that open along two sides.
6. Pineapples are multiple fruits, consisting of many carpels derived from an inflorescence of several flowers.
7. Plums and grapes are drupes: fleshy fruits with a single seed enclosed by a stony endocarp.