ChloeYeo
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Q. Mosses are small plants with no true roots. Each plant is anchored by simple root-like structures which do not contain vascular tissue.

The leaves of moss plants are usually one cell thick and are attached to a thin stem. Neither the leaves nor stem contain vascular tissue.

(a) Suggest and explain how the absence of vascular tissue might affect the size to which moss plants can grow (2 marks).

Official answer from mark scheme:
- Cannot grow tall/large/big (1 mark)
- no support from vascular tissues/vascular bundles (1 mark)
- use only diffusion/ no mass flow/ no rapid transport (1 mark)
- diffusion is too slow (to enable substances to move large distances) (1 mark)

My answer:
- It will limit the maximum size to which plant can grow.
- sucrose and water will not be transported separately so this will reduce the water potential gradient between inside and outside plant cells. So less water will be supplied to individual cells.
- This means there is less photosynthesis, so plants grow less.
- - - - - - -----------------------------------------------------------------------------------------

I understand the mark scheme answer and I know it is right,
and I don't understand why my original answer was wrong either(
1. Why is it wrong??
and when I was first answering, I couldn't come up with the mark scheme answers
2. how do you come up with the mark scheme answer straight away?
is there any sub topic in plants that you have to know in detail?

Thank you so so much.
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niaphonic
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Hello!

I tutor Biology, so hopefully this helps..

(a) Suggest and explain how the absence of vascular tissue might affect the size to which moss plants can grow (2 marks).

I think you've overthought your answer - your first suggest point is right! and if you had explained why it would limit the maximum size to which a plant can grow, I would have given you both marks.

You need to suggest how the absence of vascular tissue might affect the size to which the moss plants grow (you correctly said it would limit the maximum size to which they can grow), but then you need to explain why this would be the case (i.e. there would be no vascular tissue/vascular bundles to support it as it grows).


Usually with these questions, the mark scheme will specify that you can only be awarded both marks if you suggest a point and explain it.


Have a look at the mark scheme again - the first two marking points relate to one possible answer, and the other two relate to another possible answer.

- Cannot grow tall/large/big (1 mark) [suggest]
- [because] no support from vascular tissues/vascular bundles (1 mark) [explain]

- use only diffusion/ no mass flow/ no rapid transport (1 mark) [suggest]
- [because] diffusion is too slow (to enable substances to move large distances) (1 mark) [explain]



I think that you've tried to think about the question more deeply than they want you to!
There's no trick to getting the mark scheme answer first time (as the mark schemes are written based on the answers that students give in the exam paper that year), but try to keep your answers simple - they're (usually) not trying to catch you out, and you know all that you need to know.

The key point here is that vascular tissue in plants allows the rapid transport of substances, meaning that they do not have to rely on diffusion alone (which would not allow them to grow as large). And, that vascular tissue has a structural role to play, in physically supporting the plant as it grows larger.
You don't need to go more in depth than this for the two marks
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