Chapter 3 – Functioning of organisms: green plants
Consider the following statements and click to reveal the answer.
1. What common names are given to the two major groups or classes of flowering plants?
The monocotyledonous plants (Liliidae) and dicotyledonous plants (Magnoliidae) are better known simply as monocots and dicots.
2. What is the significance of the mnemonic ‘Mrs Gren’?
Mrs Gren is a mnemonic formed from the first letters of the life processes as they are presented here. Mnemonics are useful memory aids.
3. How are plant and animal cells different?
Plant and animal cells have many similarities but differ in certain key respects. Animal cells do not have cellulose cell walls, chloroplasts or large, permanent vacuoles.
4. Using your knowledge and understanding of light and colour, explain why green plants are green.
Chlorophyll reflects the green component of visible or white light. Most of the energy absorbed is from the blue and red ends of the spectrum.
5. What are the main functions of the following?
Roots anchor plants. Stems hold plants upright, keep leaves and flowers spread out, store starch and provide links between roots and shoots. The leaves of plants are where photosynthesis takes place. Flowers are reproductive structures.
6. What is photosynthesis, why is it important and where does it normally take place?
Photosynthesis is the process by which plants make their own food. Without the energy from food, plants, like all other living organisms, would soon die. Photosynthesis takes place mostly in the leaves of plants, though all green tissues are capable of photosynthesis.
7. Which factors limit the rate at which photosynthesis takes place?
The rate of photosynthesis is affected by light intensity, temperature, the concentration of carbon dioxide in air and water availability.
8. How do phloem and xylem cells differ from other plant cells?
Phloem cells are connected together by perforated end walls or sieve plates. They have no organelles including a nucleus and no vacuoles. Xylem cells are dead. Their cell walls often contain lignin, which provides support.
9. Why can seeds germinate and grow in the dark but fully grown plants cannot?
Seeds germinate in the dark because they are able to draw on their own stored food reserves. In dicot plants, for example, food is stored in each of the two cotyledons. Fully grown plants need light in order to photosynthesise.
10. Why do you think that the widespread use of herbicides, insecticides and fungicides causes so much concern?
Herbicides, insectides and fungicides contain chemicals which not only kill off the organisms causing problems but many others too. They are not always selective. Dead or alive, organisms sprayed with pesticides can find their way into and contaminate different trophic levels of food chains. Some organisms eventually become resistant to chemicals.
11. Sketch a flowering plant. Label the roots, stem, leaves and flowers and describe the main function of each of these. Produce a sketch of a flower in more detail, showing the male and female reproductive organs. In a flowering plant, how does sexual reproduction take place?
Sketches and labelling will vary. Check against text and chapter illustrations. Reproduction takes place in five well-defined stages: pollination, fertilisation, seed formation, seed dispersal and germination.
12. What are the limiting factors for seed germination and photosynthesis?
Seed germination can be affected by water availability, temperature and oxygen but not usually light. Photosynthesis can be affected by light, temperature, carbon dioxide concentration and water availability.
13. Design as many different investigations or experiments to test each one as you can. Begin by predicting outcomes and stating the hypotheses that you wish to test.
Investigations or experiments may vary. If seeds do not usually need light to germinate, for example, this can be tested easily by germinating them in suitable locations (‘Do seeds usually need light to germinate?’). Investigations or experiments with oxygen and carbon dioxide are generally not suitable for the primary classroom.