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17 Cards in this Set
- Front
- Back
When is Meiosis involved? |
During: 1. Crossing Over 2. Production of Gametes. |
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The pollen tube grows from the pollen grain to the micropyle. Suggest onestimulus, other than water, that causes the pollen tube to grow towards themicropyle.
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Chemical, air, gravity, light. |
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The tip of the growing pollen tube releases digestive enzymes into the style.Suggest the role of these digestive enzymes in the growth of the pollen tube.
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1. idea of {breakdown / digestion / eq} of style ;2. (breaks down) protein / pectin / middlelamella 3. reference to hydrolysis / 4. easier for pollen tube to grow / reducedresistance 5. supplies {nutrients / named nutrient / energy}for (pollen tube) growth |
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Give three roles of water in a plant other than for pollen tube growth.
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1. Photosynthesis. 2. Water as a solvent. 3. Water as a transport medium. 4. Role in structural support. 5. Involvement in hydrolysis. 6. Thermogredulation. |
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In the second fertilisation, the other male gamete nucleus fuses with twopolar nuclei forming a triploid structure. Name the triploid structure formed
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Endosperm nucleus. |
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Suggest the advantages to flowering plants of increased pollen tube growth.
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1. more likely to reach the ovule
2. fertilisation more likely to occur 3. idea of fertilisation in shorter time period |
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Name the type of cell division required for asexual reproduction.
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Mitosis |
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Describe and explain why asexual reproduction results in low genetic diversity.
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1. low genetic diversity is less different alleles in the gene pool.
2. (asexual reproduction leads to) all offspring being{genetically identical / clones / same genotype / samealleles 3. no meiosis/ no recombination of genetic material 4. idea of variation only possible as a result of mutation |
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Explain the function of the pollen tube in fertilisation in flowering plants.
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1. idea of {forms a pathway/ grows down through thestyle
2. grows towards { ovary / ovule / micropyle / egg cell 3. reference to digestive enzymes; 4. transports {generative nucleus / haploid nuclei / malegametes / 5. fuses with embryo sac (membrane) / tip breaks downwhen it enters the micropyle / allows male nuclei toenter embryo sac |
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Describe what happens to each of these two male nuclei.
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1. One (nucleus) fuses with the {egg nucleus / femalegamete }
2. one (nucleus) fuses with the (two) polar nuclei |
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Explain how Meiosis gives rise to genetic variation in gametes. |
1. Both independent /random assortment and {crossing-over/chiasma(ta)
2. Independent assortment gives riseto new / different combinations of (paternal andmaternal) chromosomes 3. crossing over involves swapping of{sections / eq} of {chromatids/chromosomes} ; |
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Describe the process of fertilisation that takes place in flowering plants. |
1. Idea that generative nucleus dividesto form two male gametes
2. by mitosis 3. pollen tube fuses with embryo sac 4. reference to double fertilisation 5. (one) male { gamete / nucleus }fuses with egg (cell) nucleus 6. to produce diploid zygote 7. other male nucleus fuses with twopolar nuclei 8. to produce triploid endosperm |
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Explain how meiosis produces genetic variation in gametes.
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1. Independent /random } assortment and {crossing-over/chiasma(ta) }
2. Independent assortment gives riseto {new / different / eq}combinations of (paternal andmaternal) chromosomes 3. crossing over involves swapping of{sections / eq} of {chromatids/chromosomes |
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Explain the importance of meiosis in the production of gametes.
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1. Halves the chromosome number
2. to produce a haploid nucleus 3. so that at fertilisation the {fullcomplement / diploid number ofchromosomes is restored / eq 4. allows genetic variation (in gametes) 5. through independent assortment / 6. through crossing over |
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Explain how the pollen tubes grow through the style of the flower.
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1. idea of enzymes being {produced / released / secreted
2. idea of these enzymes being used to {digest / break down /eq} (tissues of style) 3. idea of forming a pathway |
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Describe how the structure of a pollen grain differs from that of a sperm cell.
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1. pollen grain does not possess flagellum
2. pollen grain does not have an acrosome 3. idea of {more / 2 / 3} nuclei in pollen grain 4. idea of difference in outer boundary e.g. exine in pollengrains |
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Explain how meiosis can give rise to genetic variation in the gametesproduced.
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1. Crossing over and { independent/ random} assortment
2. description of crossing over as swapping over sections of{ chromatid / DNA } 3. description of independent assortment of maternal andpaternal chromosomes 4. consequence described e.g. produces recombinants ornew combinations of alleles |