A2 Biology OCR June 2015 Revision Thread

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Plants that live in the Arctic have a relatively short growing season in which the light intensity is always relatively low. Many species growing in these conditions have a high level of anthocyanin pigments in their leaves. The combined effect of these red pigments with the green chlorophyll makes the leaves appear dark purple or black.
Suggest why this adaptation is useful in increasing photosynthetic rates.

How do you answer this?

Black is a good absorber of light/heat energy, so having dark leaves maximises volume of light energy absorbed by plant during it's short growing season.

Seems more like a Physics answer though...

(edited 8 years ago)

Reply 1641

TheLegalDealer

Original post by corey7695

where does glycolysis occur?

In the cytoplasm

state the exact location where steroid hormones are made in he body

Reply 1642

loperdoper

Original post by Beni24

Guys which paper do you think was the hardest? So I can have a go at doing it :smile:

BBoth of the 2011 papers. The synoptic questions really catch you out

Reply 1643

joycestick

Specification 4.3.1 m) state that TP can be used to make carbohydrates, lipids and amino acids.
Textbook pg. 64 says its GP...

can someone help? :frown:

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Reply 1644

corey7695

Original post by TheLegalDealer

In the cytoplasm

state the exact location where steroid hormones are made in he body

the cortex of the adrenal gland

define homeostasis [3]

Reply 1645

tewas

Original post by TheLegalDealer

In the cytoplasm

state the exact location where steroid hormones are made in he body

is it the adrenal cortex?

Reply 1646

TheLegalDealer

Original post by corey7695

the cortex of the adrenal gland

define homeostasis [3]

The constant maintenance of the bodys internal environment within strict limits even thought it is constantly changing ?

outline what happens to pyruvate in yeast in anaerobic conditions

Reply 1647

coolerthanbeans

Original post by s.c.a1

does anyone know what they mean by polygenic genes in the continuous and discontinous variation spread to me it sounded a bit like epistasis or codominance but it said that those are only for discontinuous variation.so confused

Polygenic - caused by BOTH environment and genes, i.e. continuous variation.

Monogenic - caused by genes ONLY, i.e. discontinuous variation.

For example...
Height = continuous variation. Influenced by your genes (how tall your parents are) but also influenced by environment (type of food you eat, how much exercise you do etc)

Eye colour = discontinuous variation. Influenced by genes only. Eye colour is never changed by environmental variations ... (unless you can get some plastic surgery to change your eye colour? :wink:

)

EDIT: Ignore me, polygenic = characteristic coded for by many genes, monogenic = characteristic coded for by one gene :smile:

(edited 8 years ago)

Reply 1648

brooklyniona

Past question that I don't understand to do with respiration...

"The equation below shows aerobic respiration of compound A.
C55H100O6 + 77O2 → 55CO2 + 50H2Ocompound A
The respiratory quotient (RQ) is defined as: volume of CO2 releasedvolume of O2 absorbed|
(ii) Calculate the RQ for this reaction. Show your working."

I got 0.71 which was correct. But the next question was...
"Compound A is a fat. Suggest what the RQ of a carbohydrate such as glucose might be" The answer is 1.0 but I have no idea why! Anyone know why it's 1.0?? thanks

Reply 1649

TheLegalDealer

Original post by tewas

is it the adrenal cortex?

Yes , btw you have to say Adrenal as it asks for the specific location

Reply 1650

tewas

Original post by corey7695

the cortex of the adrenal gland

define homeostasis [3]

The maintenance of internal conditions at a constant state despite changes in the external environment

Reply 1651

maisie__x

Original post by joycestick

Specification 4.3.1 m) state that TP can be used to make carbohydrates, lipids and amino acids.
Textbook pg. 64 says its GP...

can someone help? :frown:

My revision guide says its TP and if that's what the spec says as well i'd go with that :smile:

Reply 1652

gh1290

Original post by TheLegalDealer

In the cytoplasm

state the exact location where steroid hormones are made in he body

The adrenal medulla?? not sure about that

Reply 1653

Beni24

What does a low and a high Respiratory substrate indicate? :smile:

Reply 1654

corey7695

Original post by TheLegalDealer

The constant maintenance of the bodys internal environment within strict limits even thought it is constantly changing ?

outline what happens to pyruvate in yeast in anaerobic conditions

perfect

it is decarboxylated to form ethanal, which is hydrogenated by red nad to form nad, and ethanol is formed (my book doesn't reference the enzymes, is it lactate dehydrogenase and decarboxylase?)

explain the process that occurs when the body is dehydrated

Reply 1655

TheLegalDealer

Original post by gh1290

The adrenal medulla?? not sure about that

All steroid hormones are made in the adrenal cortex and adrenaline is made in the adrenal medulla

Reply 1656

thequackingduck

Original post by corey7695

the cortex of the adrenal gland

define homeostasis [3]

Would you need to give the definition AND an example to get the three marks?

Reply 1657

tewas

Original post by brooklyniona

i think it's something that you need to know eg. carbohydrate = 1.0, fats = 0.7 and proteins = 0/9

Reply 1658

coolerthanbeans

Original post by joycestick

Specification 4.3.1 m) state that TP can be used to make carbohydrates, lipids and amino acids.
Textbook pg. 64 says its GP...

can someone help? :frown:

I think mark schemes are pretty lenient on this one, from what I've seen anyway.

GP can be used to make fatty acids and amino acids.

TP can be used to make various hexose sugars (e.g. glucose) and glycerol.

Both GP and TP would be needed to make lipids ( fatty acids from GP, glycerol from TP).
TP is needed for the carbohydrates (the hexose sugars).
GP is needed for the amino acids.

:smile:

(edited 8 years ago)

Reply 1659

corey7695