AQA BIOL2~3rd June 2013~AS Biology (Now Closed)

Original post by oak12

anyone need any help?

When you gonna sleep?

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Reply 3143

tumblrgirl

Original post by oak12

- mineral ions are actively transported into the xylem from the soil via the roots
- this lowers the water potential in the xylem
- so water follows by osmosis

- water can move in by symplast: directly thru the cells via the cytoplasm, it moves thru the root hair cell, cortex cells, endodermis cells into the xylem. the cells are connected by plasmodesmata

- water can move in by apoplast: moves between cells in the cell wall, it takes this route until the endodermis cells, where it encounters the casparin strip, which is an impermeable waterproof barrier, so it moves into the endodermis cell and into the xylem

ahh thankyou :biggrin:

Reply 3144

Original post by Tplox

When you gonna sleep?Posted from TSR Mobile

i'm staying up to help

(i recommend people to sleep, but if you're staying up for the long slog, i'm here to help)

Reply 3145

issy5038

Original post by tumblrgirl

can someone please explain the whole process of water getting into the plants by the root hair cells through to water being moved up the xylem pleaseeee? :frown:

water moves from the soil into the root hair cell down a water potential gradient by osmosis, as the cell sap in the root hair cell contains mineral ions creating a more negative water potential.
water then moves from the root hair cell through the cortex in one of two ways:
1. symplastic pathway through the cytoplasm by osmosis, through the plasmodesmata joining cells together
2. apoplastic pathway through cell walls, drawn along by cohesion tension
when the water reaches the casparian strip any water in the cell walls is forced into the cytoplasm: it can no longer continue in the apoplastic pathway.
salts are actively transported into the xylem by the endodermis, creating a more negative water potential and drawing water from the cytoplasm into the xylem.
water is then moved up the xylem by cohesion tension due to the negative pressure created by the pull of transpiration
:smile:

Reply 3146

Charlz94

1

Original post by oak12

i'm staying up to help

(i recommend people to sleep, but if you're staying up for the long slog, i'm here to help)

Just realised I'm kinda **** at meiosis. What do we actually have to know?

Reply 3147

unknown guy

can someone plez summarise potomoeter I just don't get it

also why is the shoot cut under water

why is water uptake not equivalent to transpiration

Reply 3148

Eterniity

4

Original post by oak12

i'm staying up to help

(i recommend people to sleep, but if you're staying up for the long slog, i'm here to help)

Reply 3149

Thebest786

Original post by oak12

i'm staying up to help

(i recommend people to sleep, but if you're staying up for the long slog, i'm here to help)

Meiosis:

The thing that is confusing me is, initially if we had 4 chromosomes with 2 sister chromatids each, how would they divide to become 4 cells. I know the steps and what happens in each step but I tried to draw it out and that is what confuses me.
Please can you tell me how the steps can be supported by proper diagram.

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Reply 3150

Learner_108

Anyone know the simple definitions like phylogeny, hierarchy, taxonomy, classification ?

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Reply 3151

Original post by Charlz94

Just realised I'm kinda **** at meiosis. What do we actually have to know?

ok

- meiosis involves the production of gametes with haploid chromosomes (half the full set) and genetic variation

- it produces 4 gametes

- it involves interphase, meiosis 1 and meiosis 2

- in meiosis 1: crossing over and independent assortment of homologous pairs occur

- in meiosis 2: independent assortment of chromatids occur

- independent assortment provides variation by mixing the maternal and paternal chromosomes

- crossing over provides variation by increasing the variety of alleles

Reply 3152

Tplox

Original post by Thebest786

Meiosis:

The thing that is confusing me is, initially if we had 4 chromosomes with 2 sister chromatids each, how would they divide to become 4 cells. I know the steps and what happens in each step but I tried to draw it out and that is what confuses me.
Please can you tell me how the steps can be supported by proper diagram.

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I'm not fully sure
But there is meiosis 1 and meiosis 2
So there are 2 divisions
Does that make it clearer or worse :/

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Reply 3153

Original post by unknown guy

can someone plez summarise potomoeter I just don't get it

also why is the shoot cut under water

why is water uptake not equivalent to transpiration

potometer:

- measure rate of transpiration

- does this by measuring rate of water uptake, as this is proportional to water loss (transpiration). however, water loss can also occur thru photosynthesis and being used to make the cells turgid.

- you need to make sure the shoot and leaf is healthy, the shoot is cut under water, the shoot is cut at an angle and the tubing is air and water tight

- cutting the shoot under water maintains the continuous column of water in the xylem and prevents air bubble entering and blocking it

- to measure transpiration you have to measure distance over time

Reply 3154

Thebest786

Original post by Tplox

I'm not fully sure
But there is meiosis 1 and meiosis 2
So there are 2 divisions
Does that make it clearer or worse :/

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I know there are 2 stages and what happens, but drawing out like a simulation is what is confusing me. Dont blame you mate.
Is there any way someone could put up a picture of meiosis in stages ?

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(edited 10 years ago)

Reply 3155

Tplox

Original post by Learner_108

Anyone know the simple definitions like phylogeny, hierarchy, taxonomy, classification ?

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Classification - grouping of organisms
Taxonomy - theory and practice of biological classification

Phylogeny - evolutionary relationship between organisms

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Reply 3156

Original post by Learner_108

Anyone know the simple definitions like phylogeny, hierarchy, taxonomy, classification ?

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classification = placing organisms into groups based on similarities

taxonomy = the principles by which classification occurs

hierachy = dividing large groups down into smaller groups, with no overlap

phylogeny = shows evolutionary relationships, how closely related different species are, and how common a recent ancestor they have

anyone else?

Original post by oak12

anyone else?

My meiosis question ?

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Reply 3159