plants and meiosis - BIO Flashcards
4 reasons why plants respond to stimuli?
to avoid stress
to avoid being eaten
enhance/ensure survival
to improve their chances of having offspring
model answer for a plant growing upwards towards light using auxin:
auxin is a plant ? produced at the base of the ? of the plant/shoot. When light is directly ?, auxin ? evenly down the sides of the shoot. In a shoot, auxin promotes cell ? and ? elongation. Even distribution of ? causes even growth so the shoot grows ? evenly towards light. this is called ? phototropism
hormone, tip, above, diffuses, division, cell, Auxin, upwards, positive
model answer for a plant bending diagonally towards light using auxin:
auxin is a plant ? produced at the base of the ? of the plant/shoot. When light is shining from one ?, auxin ? unevenly down the shaded side of the shoot (the side away from the ?). In a shoot, auxin promotes cell ? and ? elongation. Uneven distribution of ? causes uneven growth of the ? side so the shaded ? grows ? , causing it to bend towards ?. this is called ? phototropism
hormone, tip, side, diffuses, light, division, cell, Auxin, shaded, side, quicker, light, positive
Model answer for negative geotropism (when the shoot lays sideways)
Auxin is a plant hormone produced at the base of the tip of a plant/shoot. When the shoot lays sideways, gravity causes the auxin to fall to the lower surface. In shoots, Auxin promotes cell division and cell elongation. As there is an uneven distribution of Auxin on the lower surface, there is uneven growth (the lower side grows more quickly than the upper side) and because of this the shoot grows upwards - against gravity - hence negative geotropism
model answer for a root growing downwards towards gravity using auxin:
Auxin is a plant hormone produced in the base of the tip (in the shoot). When the shoot lays sideways, gravity causes Auxin to fall to the lower surface. IN roots, Auxin inhibits cell division and cell elongation. There is an uneven distribution of Auxin on the lower surface, so therefore there is uneven growth and the upper side/surface grows more quickly , so the root grows downwards , therefore positive geotropism.
what 6 main things do plants respond to?
humidity, light, gravity, temperature, physical touch and water
what is positive thigmotropism??
growth towards physical touch
positive/negative geotropism?
growth with(towards)/against gravity
positive/negative hydrotropism?
growth towards/away from water
positive/negative phototropism?
growth towards/away from light
plant germination required practical, key method points?
- collect 3 petri dishes,
- place 8 seedlings on cotton wool in each petri dish,
- put each dish in a different type of light - one in full light (eg: the window), one is partial light (eg: in a box with a hole cut in it), and one in darkness (eg: a closet/cupboard),
- measure the height of each seedling beforehand and record this in a table,
- then leave the petri dishes in their appropriate areas for 5 days, - - once this time is up - measure the new heights and record these in the same table.
plant germination required practical, results/hypothesis points?
- ones in full sunlight should grow the most and grow upwards - positive phototropism
- ones in partial sunlight should grow more diagonally towards the light source and slightly less so - positive phototropism
- ones in no sunlight should initially grow due to their energy source - and they naturally grow to search for light, but will then die when there is no light
plant germination required practical, key analysis points?
- draw a table of heights before and after and calculate the height difference between these two
- calculate a mean of change in height for each petri dish
- maybe also repeat experiment for increased accuracy
- draw a graph to show and compare results (maybe a bar chart) with change in height on the y axis and the light condition on the x axis
plant germination required practical, key variables points?
- control variables: same amount of seedlings, same amount of dampness and water, same light intensity, same type of seedlings
- independent variable : type of sunlight - full, partial, or none
- dependent variable(s) : change in height, how many plants have grown, direction of growth
3 ways that Auxin can help commercial farming??
can grow plant clones by adding an Auxin growth medium, can grow cuttings using rooting powder (which contains Auxin), can use Auxin in weedkillers as it can disrupt the plant’s growth patterns
3 ways that Giberrellins can help commercial farming??
can expose plants to it to induce germination as it controls plant dormancy ( allowing farmers to grow mutliple crops per year and at better times), can make more or bigger flowers, and can make fruit especially seedless ones grow bigger fruit
ways that Ethene can help commercial farming??
it can control the ripening process, so people pick the fruit before it’s ripe, so it doesn’t decompose while travelling and then expose to ethene with big Ethene chambers. However plants can often produce their own ethene so they block this by chilling it or blocking with a chemical inhibitor.
what happens in interphase?
the organelles duplicate, as well as the DNA - so there are 4 chromatids (but still 2 chromosomes - one mother, one father)
what happens in prophase?
each chromosome is made of 2 sister chromatids, nuclear membrane disappears and spindles start to form
what happens in metaphase?
homologous chromosomes line up on equator of cell, and spindle fibres attach to chromosomes
what happens in anaphase?
chromatids are pulled to opposite poles by the spindle fibres
what happens in telephase? (Mitosis)
nuclear envelope reforms around each new nuclei, each chromosome still had two chromatids - end of mitosis
what happens after mitosis and what is it called?
cytokinesis - the membrane divides to give 2 genetically identical daughter cells, chromosome number stays the same, and cytoplasm and cell membrane divides!
what main thing happens at meiosis and why?
4 genetically different gametes are produced from 1parent cell - with half the number of chromosomes - this is because two gametes fuse together in fertilisation so if they fused with a full amount of chromosomes they would have 92 chromosomes which is too much and would lead to an increased risk of miscarriage in human sexual reproduction.
what happens if a cell has a chromosome from both the maternal and paternal cell?
the cell is diploid
examples of homologous chromosomes?
the maternal and paternal genes that code for the same genes
what happens in meiosis after cytokinesis 1
this forms two haploid daughter cells - only one chromosome! prophase 2 : the nuclear envelope disappears and spindle fibres reform
what happens in meiosis after prophase 2
metaphase 2 - chromosomes line up on equator
what happens in meiosis after metaphase 2
anaphase 2 -chromatids are pulled to opposite poles by the spindle fibres
what happens in meiosis after anaphase 2
telophase and cytokinetis 2 - nuclear membranes reform around the chromosomes. then cytokinesis occurs to form 4 granddaughter cells
what does cytokinesis 2 make?
4 haploid daughter cells which are genetically different from one another and the parent cell - and only have 23 chromosomes
what is different in the first anaphase inmitosis compared to meiosis
in mitosis - the chromatids are pulled to the poles by the spindle fibres but in meiosis the pairs of chromosomes are pulled to the poles by the spindle fibres
2 ways meiosis creates genetically different daughter cells by creating variation?
- recombination/cross over where there is an exchange of DNA between chromatids from homologous - so chromosomes are no longer genetically identical
- random fertilisation where an sperm could fertilise any egg and so therefore random combinations of genetic material
purpose of mitosis vs meiosis
to repair body cells, to form gametes
how many chromosomes are in a daughter cell comapred to a parent cell?
1. mitosis
2. meiosis
- same - 46
- half - 23
Sexual reproduction :
- Involves ? to form the gametes - egg and ?
- At ? , the gametes (sex ? ) fuse - each gamete has ? a set of genetic information - so they are ?
- After fertilisation, the embryo divides by ?
- This requires ? parents
- Variation is introduced by crossing ? and due to ? fertilisation - producing genetically ? offspring
meiosis, sperm
fertilisation, cells, half, haploid
mitosis
two
over, random, different
Asexual reproduction:
- Involves ? only
- Only needs ? parent
- No fusing of sex ?
- Offspring are ? identical to parent ?
mitosis
one
cells
genetically, CLONES
2 main pros of sexual reproduction?
- variation - means some offspring are likely/ able to survive environmental changes : evolution
- new variation means some offspring can colonise (and survive in) new location
3 main cons of sexual reproduction?
- variation could lead to some offspring being less able to survive certain conditions
- 2 parents - means it is time consuming or energy inefficient to find a mate
- energy costly to make gametes
5 main pros of asexual reproduction?
- 1 parent - so no time or energy wasted finding a mate
- faster (as mitosis has one division whereas meiosis has two)
- not making gametes - so easier
- lots of identical offspring produced in favourable conditions
- clones could have economic benefits
main con of asexual reproduction?
no variation - so if all offspring are identical they may all be at risk to new environmental changes
what 4 organisms can carry out both sexual and asexual reproduction?
plasmodium, fungi, strawberry, daffodils
what is plasmodium?
the parasite involved in malaria
when does the parasite plasmodium divide asexually and when does it divide sexually?
- asexually - when it’s in the human host (mitosis)
- sexually - when it’s in the vector/mosquito (meiosis)
when does fungi divide asexually and when does it divide sexually?
- in favorable conditions, fungi produce spores via asexual reproduction- and these spores are spread by wind or water - which colonize areas and matured to give adult fungi
when does the strawberry divide asexually and when does it divide sexually?
- reproduces sexually via pollination
- reproduces asexually when strawberry plants produce runners and new genetically identical strawberry plants form along them
when does the daffodils divide asexually and when does it divide sexually?
- reproduce sexually via pollution
- reproduce asexually (mitosis) - when new genetically identical bulbs form on the older bud and these bulbs can be divided and replanted!
why may there be variation in organisms produced by asexual reproduction?
as although they are genetically identical, there may be variation due to the environment, eg: lack of water, nutrients in soil like ions, light intensity, humidity and space!!!
