Nelson Biology VCE Units 1 & 2. Answers to Chapter Questions. Chapter 6

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1 Nelson Biology VCE Units 1 & 2 Answers to Chapter Questions Chapter 6 Review questions 1 Organisms produced by asexual reproduction carry identical DNA and therefore are genetically identical; thus they are clones, as clones are genetically identical to each other. 2 When a species finds itself located in an inhospitable environment and one variety appears to thrive, there are characteristics that one variety possesses that make it survive best. In this situation, producing identical offspring to exploit the environment is of great advantage to that species. 3 Four methods of asexual reproduction: Name of method Description of method Example Fragmentation Budding Spores Vegetative propagation An organism is broken into two or more pieces and then each piece is able to regenerate a complete individual. An outgrowth from the parent organism can detach and form a new individual. Single-celled bodies form as a result of cell division in parent organisms. A complete new organism is produced from a cutting off the parent plant. Sponges Hydra Ferns Potatoes, carrots 4 Similarities and differences between fragmentation and vegetative propagation: Fragmentation Vegetative propagation Similarities A complete new organism can arise from a piece of the parent plant. Differences A piece of the organism can be pulped and passed through fine gauze and an individual will form from cells coming together. A piece of the original organism must be able to divide and needs to remain as complete piece in order to take root. A piece of an organism can be grafted onto another and it will grow. Nelson Australia Pty Ltd

2 5 Bacteria reproduce by binary fission and division of bacterial cells can occur every 20 minutes, so in a 24-hour period a single bacterial cell can give rise to a population in excess of 4000 million cells. 6 Sexual reproduction occurs when two parents of opposite gender produce gametes that, when combined in fertilisation, give rise to a genetically unique individual. This individual carries half the DNA of one parent and half the DNA of the second parent. This differs from asexual reproduction in that only one parent organism is required in asexual reproduction and cells do not fuse to give rise to offspring. 7 Sexual reproduction gives rise to variety in individual features within the one species. Some features are more advantageous in a particular environment than others. If conditions change within an organism s habitat the variety within the group should allow at least some individuals to survive and go on to reproduce. 8 Gametes are produced when meiosis occurs in the reproductive cells of the organisms. Meiosis ensures all gametes produced give rise to cells with half the genetic material of the parents. 9 Fertilisation is the process that restores the full species chromosome number. 10 Refer to Figure The advantages of being able to reproduce both sexually and asexually are that in ideal environmental conditions asexual reproduction ensures the quick production of many offspring that are able to take advantage of the best conditions. Conversely, in adverse conditions the variety offered in sexual reproduction ensures the survival of at least some members of a population. 12 Purpose of flowering parts: Part Flower Petals Stigma Anther Pollen tube Purpose Location of both male and female reproductive structures To lure potential pollinators to the flower to collect pollen To ensure the securing of the pollen once it lands on the sticky surface Produces and stores the pollen Ensures the pollen reaches the ova that are to be fertilised 13 Answer should include: a description of the production of both male and female gametes the transfer of the pollen from the anther to a stigma. 14 Meiosis would occur in the anthers to produce the pollen and in the ovule to produce the ova. 15 Pollen and ova each have half the genetic complement of the other cells in the plant. Nelson Australia Pty Ltd

3 16 Self-pollination of flowers reduces the variety possible and a reduction in the chances of survival of the species in unfavourable conditions. 17 Different pollination methods: Method Supportive plant structure Wind pollination Very light-weight pollen and very sticky stigma Insect pollinators Great supplies of nectar and floral displays 18 Students need to use terms from the key terms to put together their own concept map, beginning with pollination and ending with seed germination. 19 Internal and external fertilisation: Internal fertilisation Sperm meets egg in a protected environment therefore the organism requires only small numbers of gametes, particularly ova. Fertilised eggs have a protected area in which to develop. Fewer offspring are produced at one time, so some parenting may occur. External fertilisation Great numbers of gametes are produced at one time, providing a greater possibility of fertilisation occurring. Fertilised eggs are at greater risk of not maturing, as they are left to the elements. Many offspring are likely to survive, with little chance of parenting behaviour. 20 The hormone thyroxine is thought to play a role in the metamorphosis of frogs from tadpoles to the adult croaker. Thyroxine appears to turn on the genes responsible for the development of the tadpole into an adult. 21 Students need to use Figure 6.30 and the accompanying text to complete this task. 22 The semen provides energy for sperm locomotion and a transport medium through the male reproductive organs after the production of sperm. 23 The two main functions of the testes are to produce the hormone testosterone and produce sperm. 24 Major female reproductive organs: Organ Function Ovary The location of egg formation; produces oestrogen and progesterone Oviduct/Fallopian tube Connects the ovary to the uterus; location of egg fertilisation Uterus Where the embryo develops; lined with endometrium Vagina The canal through which the young is born; location of release of sperm from penis during sexual intercourse. Nelson Australia Pty Ltd

4 25 Main female hormones: Hormone Production location Effect Oestrogen Ovary Stimulates the development of secondary sexual features in the female Progesterone Ovary Thickens the uterus lining (endometrium) Follicle stimulating hormone (FSH) and luteinizing hormone (LH) Pituitary gland FSH stimulates the eggs to mature in the ovary and LH causes the egg to be released. 26 The three phases of the menstrual cycle are: the follicular phase, which is the first 14 days of the menstrual cycle and involves the maturation of the follicles ovulation, which occurs around day 14 and involves the release of the egg from the ovary the luteal phase, which is the period where the endometrium is being built up in the uterus. 27 Fertilisation occurs in the Fallopian tubes and implantation takes place in the uterus. 28 Each of the gametes contains one set of chromosomes. At fertilisation, the nuclei of the egg and sperm fuse and in this way the new individual has the full complement of chromosomes for the species. 29 When the gametes come together and their nuclei fuse, a zygote is formed. The zygote then divides by mitosis and forms a solid mass that implants into the uterus wall; it then is called an embryo. After 8 weeks of development the embryo is known as a foetus. 30 The embryo does not interact directly with the external environment; however, it receives its nutrients through the umbilical cord, which is attached to the placenta. Nutrients, gases and wastes cross the placenta by diffusion. 31 Marsupials do not have a placenta, so the young are born at a very underdeveloped stage and then reach maturity inside the mother s pouch. The gestation period for marsupials is very short. 32 A sexual cycle describes the time of the menstrual cycle in human females or the period from one ovulation episode to the next in other mammals. 33 The main difference between the oestrus cycle and the menstrual cycle is that no menstruation takes place in mammals that experience the oestrus cycle. Apply understanding 1 Organisms that reproduce asexually through budding are unlikely to have a large number of specialised cell types because the new organism develops from a mature cell(s) that can only reproduce themselves. Nelson Australia Pty Ltd

5 2 Spirogyra reproduce asexually in environments that are ideal and the organism exploits these conditions by reproducing very quickly. If conditions are ideal then the organism will reproduce asexually. Conversely, when conditions may be difficult sexual reproduction offers a greater diversity in the offspring, and to ensure the survival of the species it is advantageous to produce offspring with variety. If conditions are less than ideal then the organism will reproduce by sexual means. 3 The number of offspring produced is a survival strategy that ensures that at least some individuals will survive to adulthood and reproduce also. The large numbers occur in species where there may be little parenting of the young; therefore the young are left to their own devices to survive. In the cases where fewer young are produced there is probably some parenting behaviour and a stage in childhood where the offspring spend time with their parents learning how to survive in the world. 4 The species ensures that members of the next generation are able to survive in the world and fend for themselves before they produce their own offspring. In this way, if some parenting is required, the parents know what to do. 5 The availability of resources is a determining factor. Plants that produce seeds are putting their genes away for a rainy day. When conditions are more suitable the seed will sprout and take advantage of the conditions. A plant that grows in a forest is able to access the resources and these enable it to sustain itself. 6 Arguments for the statement the hen is the egg s means of ensuring the survival of the egg include the one that females produce eggs that are laid when the shell is best developed, therefore providing the chick with the best opportunity of hatching. Arguments against the statement might include one saying that the egg takes a great many resources that could be better used to aid the survival of the species. 7 Least to most variation is: (d), (a), (c), (b). Investigate and inquire 1 The sex cells of mosses require moist conditions so that they are able to meet and join in fertilisation. The sex cells are not protected and do not meet inside any structures provided by the plant. 2 The answer should include the fact that self-fertilisation will not increase genetic diversity or the distribution of the plant species. If self-fertilisation was to occur, and the plant was genetically diseased, then all the offspring might inherit the condition. Students should research examples from both plants and animals. 3 Fungi reproduce by spores. These structures are quite resilient in adverse conditions and therefore do not sprout unless located in the most ideal of environments. When they do sprout it is because they are in an environment that will provide all their needs. Nelson Australia Pty Ltd