Chapter 16 Flashcards
Reproduction (12 cards)
Describe asexual reproduction
a process resulting in the production of genetically identical offspring from one parent
Example of asexual reproduction in bacteria, fungi and potatoes
!! refer to diagrams 16.1 !!
bacteria: binary fission → DNA replicates → cell divides into two → each daughter cell contains a copy of the parental DNA
fungi: produce spores → inside a structure (sporangium). when ripe sporangium bursts → disperse spores → in suitable conditions germinate and grow to form new fungi
potatoes: stem tubers → parent plant photosynthesizes and stores the food produced in underground stems → swell to form tubers each storing starch → buds in depressions in the surface (called eyes) → in suitable conditions buds use the stored food to form shoots from which roots also develop→ each tuber can form a new plant
Explain the advantages of asexual reproduction
quick process → only one parent needed → no gametes needed → all good characteristics of the parent are passed on to offspring (genetically identical offspring)
– when there is no dispersal (e.g. in potato tubers), offspring will grow in the same favourable environment as the parent
– plants that reproduce asexually usually store large amounts of food that allow rapid growth when conditions are suitable
preserve desirable qualities in crops: the good characteristics of the parent are passed on to all the offspring; the bulbs produced can be guaranteed to produce the same shape and colour of flower from one generation to the next, young plants grown can be transported much more cheaply than, for example, potato tubers, as the latter are much bulkier → as growth of new plants by asexual reproduction tends to be a quick process
Explain the disadvantages of asexual reproduction
– less variation → adaptation to a changing environment (evolution) is unlikely
– if the parent has no resistance to a particular disease, none of the offspring will have resistance → if the climate or other conditions change, or a vegetatively produced plant has no resistance to a particular disease, the whole population could be wiped out
– lack of dispersal (e.g. potato tubers) can lead to competition for nutrients, water and light
Describe sexual reproduction
a process involving the fusion of the nuclei of two gametes
to form a zygote and the production of offspring that are genetically different from each other
Describe fertilisation
fusion of the nuclei of gametes (haploid) to form a zygote (diploid)
Explain the advantages of sexual reproduction
– variation in the offspring, so adaptation to a changing
or new environment is likely to occur, enabling survival of the species
– new varieties can be created, which may have resistance to disease
– in plants, seeds are produced, which allows dispersal away from the parent plant, reducing competition
Sexual reproduction is exploited in agriculture and horticulture to produce new varieties of animals and plants by cross-breeding which can have the combined features of the organisms used to produce them.
Explain the disadvantages of sexual reproduction
– two parents are usually needed (although not
always – some plants can self-pollinate)
– growth of a new plant to maturity from a seed
is slow
Describe pollination (self and cross)
the transfer of pollen grains from an anther to a stigma
– self: transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant
– cross: transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
Discuss the potential effects of self-pollination and cross-pollination on a population
self: increases the chance of fertilization & seed formation, but reduces variation in the offspring – less likely to be able to adapt to cope with environmental change
cross: reduces the chance of fertilization (wind-pollinated flowers produce large numbers of pollen grains because of the wastage involved), but increases variation and the ability to adapt to environmental change
Distinguish between the pollen grains of insect-pollinated and wind-pollinated flowers
!! refer to diagram 16.4 !!
petals:
insect – often large, coloured and scented, with guidelines to guide insects into the flower
wind – absent, or small and inconspicuous
nectar:
insect – produced by nectaries to attract insects
wind – absent
stamen:
insect – present inside the flower
wind – long filaments – anthers to hang freely outside the flower – expose pollen to wind
pollen:
insect – smaller numbers of grains = round and sticky, or covered in spikes to attach to the furry bodies of insects
wind – larger numbers of smooth and light pollen grains, which are easily carried by the wind
bracts (modified
leaves):
insect – absent
wind – sometimes present
Describe the structures in plants that relate to sexual reproduction
sepals: protects the flower while in bud
petals: often large and coloured to attract insects
stamen: male reproductive part – anther + filament
filament: supports the anther
anther: contains pollen sacs in which pollen grains are formed – pollen contains male sex cells (gametes)
carpel: female reproductive part – stigma, style, ovary
style: links the stigma to the ovary; through which pollen tubes grow
stigma: sticky surface that receives pollen during pollination
ovary: contains ovules
ovules: contains a nucleus, which develops into a seed when fertilized
