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URGENT! Help needed on biology questions

Hi,
I've got an exam this week and I've been going through some past papers. Could anyone help me with these questions?

1. Nitrogen fixing
denitrifying
nitrifying
decomposing

How many of these bacteria help plants to grow?

2. Amount of nitrate fertiliser added (kg per hectare): top line
amount of crop produced (tonnes per hectare) :bottom line

0 50 100 150 200 250 300
4 6 7 8 9 9 8

The best interpreatation is that:

A - crops can grow only if nitrate is added to the soil
B - the more nitrate added the more crop will be produced
C - nitrate is not the only factor that helps crops to grow
D - too much nitrate kills crops

3. An animal cell placed in concentrated salt water will:

A - swell and burst
B - stay the same size
C - shrink
D - shrink and burst

Reply 1

rahmed

3. C - Because of osmosis. The outside contains less water than the inside of the cell, hence setting up an osmotic gradient. Water will therefore leave the cell, causing it to shrink. It won't burst obviously.

Reply 2

j00ni

minnie

2. Amount of nitrate fertiliser added (kg per hectare): top line
amount of crop produced (tonnes per hectare) :bottom line

0 50 100 150 200 250 300
4 6 7 8 9 9 8

The best interpreatation is that:

A - crops can grow only if nitrate is added to the soil

False - as 4 tonnes are produced in the absence of any fertiliser

B - the more nitrate added the more crop will be produced

False - 250kg/hct produces more crops than 300kg/hct

C - nitrate is not the only factor that helps crops to grow

True - as crops grow in the absence of fertiliser

D - too much nitrate kills crops

Possibly True, more data needed - since 300kg/hct has a lower yield it could be postulated that increasing fertiliser beyond 250kg/hct kills crops, but this would need to be tested to be sure

Therefore C is the best fit