HSC Biology Question Thread

[kevin217]

Hey guys could someone simplify the move of materials in xylem and phloem. I'm having trouble understanding this dotpoint.

[aimbotted]

Hey guys could someone simplify the move of materials in xylem and phloem. I'm having trouble understanding this dotpoint.

is this the pressure flow theory and the transpiration stream theory?

[marynguyen18]

Hey guys could someone simplify the move of materials in xylem and phloem. I'm having trouble understanding this dotpoint.

xylem is dead and transports water and dissolved ions it only goes down towards the roots, whilst phloem is alive and transports water and minerals and travels both up and down. I hope that made sense

[Skidous]

Hey guys could someone simplify the move of materials in xylem and phloem. I'm having trouble understanding this dotpoint.

Xylem: Cohesion-Adhesion-Tension Theory

Step 1: Water enters the plant through the root hairs via osmosis
Step 2: As a water molecule transpires in the leaves, another one is ‘pulled up’ the column of water in the xylem by the negative pressure (tension) created to replace it.
Step 3: Another water molecule enters the plant by osmosis at the bottom of the xylem to replace the one that was lost through transpiration.
Cohesion is prevalent through the water molecules sticking together, adhesion is the water molecules adhering to the cellulose molecules of the xylem wall.   


Phloem: The Pressure-Flow Theory

Step 1: Loading at the Source
Amino acids, sucrose and other mineral nutrients are loaded into the phloem in the leaves. There are two theories as to how this may occur:
1. symplastic loading—sugars and other nutrients move in the cytoplasm from the mesophyll cells to the sieve elements through plasmodesmata (strands of cytoplasm that pass through pits in the cell walls)
2. apoplastic loading—sugars and nutrients move along a pathway through the cell walls until they reach the sieve element. They then cross the cell membrane to enter the phloem tube. These sugars pass into the sieve cell by active transport.
As sugars enter the phloem, the phloem sap becomes more concentrated and so the osmotic pressure at the source end is high. This draws water into the phloem, from the adjacent xylem tissue, by osmosis

Step 2: Offloading at the sinks
Materials flow to the sink. At the sink (for example roots, flowers or any other parts of the plant that need nutrients), sugars and materials are removed from the phloem by active transport.As sugars move out of the phloem, they draw water out with them (by osmosis). This results in a lower osmotic pressure (due to the higher water concentration) in the phloem at the sink region.

Step 3: Pressure Flow
This difference in osmotic pressure between the source and the sink in the phloem drives the phloem sap to flow. The direction of flow depends on where the sink areas (roots or flowers) of the plant are, in relation to the source (leaves). Water can move into the phloem by osmosis at any point along the gradient. The flow is continuous, because sucrose is continually being added at one end and removed at the other

Hope this helps

[Justina Shehata]

How well does someone have to perform in Biology to hit band 6's because a previous student was getting band 6's all year and performed really well in the HSC but did not get band 6 at the end of the year

[Skidous]

How well does someone have to perform in Biology to hit band 6's because a previous student was getting band 6's all year and performed really well in the HSC but did not get band 6 at the end of the year

That shifts around year to year but a scaled mark of around 90 is a band 6 but that mark of 90 can change depending on how every student does on that particular exam that year and then the marks are shifted. I.e. 2014 band 6 may be 95 but 2015 band 6 may be 87.
The best way to get band 6 is to aim for the highest mark you could possible get and then it's decided from there

[Justina Shehata]

Can anyone help me with myopia and hyperopia. Im quite confused because from what I understand is that myopia results from an elongated eyeball  but I thought to see long distance objects you needed a elongated eyeball and for close objects a more rounded eyeball? So if it results from an elongated eyeball, shouldn't there be a longer focal length and thus the image would fall behind the retina not in front?
Thank you

[Skidous]

Can anyone help me with myopia and hyperopia. Im quite confused because from what I understand is that myopia results from an elongated eyeball  but I thought to see long distance objects you needed a elongated eyeball and for close objects a more rounded eyeball? So if it results from an elongated eyeball, shouldn't there be a longer focal length and thus the image would fall behind the retina not in front?
Thank you

If your eyeball is elongated the the refractive powers of the relaxed lens would not be sufficient to refract the light into the retina but just in front of it (the lens is only part of the eyeball) and thus causing the image to be blurry when light from an object enters the eye from a far distance which I known as myopia (short-sightedness)
When dealing to looking at objects close up and far away it is actually the lens that changes shape not the eyeball. This is known as Accommodation
When an object is closer, the light scatters more from that object, hence the ciliary body contracts which causes the suspensory ligaments to loosen and thus cause the lens to increase in curvature and achieving maximum accommodation.
When an object is further away, the light from the objects are more parallel, therefore the ciliary body relaxes, causing the suspensory ligaments to tighten and thus decreasing the curvature of the eye and minimum accommodation.

Hope this helps

[kevin217]

Xylem: Cohesion-Adhesion-Tension Theory

Step 1: Water enters the plant through the root hairs via osmosis
Step 2: As a water molecule transpires in the leaves, another one is ‘pulled up’ the column of water in the xylem by the negative pressure (tension) created to replace it.
Step 3: Another water molecule enters the plant by osmosis at the bottom of the xylem to replace the one that was lost through transpiration.
Cohesion is prevalent through the water molecules sticking together, adhesion is the water molecules adhering to the cellulose molecules of the xylem wall.   


Phloem: The Pressure-Flow Theory

Step 1: Loading at the Source
Amino acids, sucrose and other mineral nutrients are loaded into the phloem in the leaves. There are two theories as to how this may occur:
1. symplastic loading—sugars and other nutrients move in the cytoplasm from the mesophyll cells to the sieve elements through plasmodesmata (strands of cytoplasm that pass through pits in the cell walls)
2. apoplastic loading—sugars and nutrients move along a pathway through the cell walls until they reach the sieve element. They then cross the cell membrane to enter the phloem tube. These sugars pass into the sieve cell by active transport.
As sugars enter the phloem, the phloem sap becomes more concentrated and so the osmotic pressure at the source end is high. This draws water into the phloem, from the adjacent xylem tissue, by osmosis

Step 2: Offloading at the sinks
Materials flow to the sink. At the sink (for example roots, flowers or any other parts of the plant that need nutrients), sugars and materials are removed from the phloem by active transport.As sugars move out of the phloem, they draw water out with them (by osmosis). This results in a lower osmotic pressure (due to the higher water concentration) in the phloem at the sink region.

Step 3: Pressure Flow
This difference in osmotic pressure between the source and the sink in the phloem drives the phloem sap to flow. The direction of flow depends on where the sink areas (roots or flowers) of the plant are, in relation to the source (leaves). Water can move into the phloem by osmosis at any point along the gradient. The flow is continuous, because sucrose is continually being added at one end and removed at the other

Hope this helps

I'm still confused on the phloem part. Is sugar still being moved in step 3? In step 2 the sugars are already actively transported to the areas of the plant where they are needed. Shouldn't the theory end here?

[RuiAce]

Not a question but just a reminder
THE HSC REQUIRES YOU TO USE BLACK PENS

If any of you guys who still have to buy pens and other materials for the exam please keep this in mind to make sure you don't waste your moneys

Good luck to all for the English Exams coming up and then the Bio exam after that

Should post that impact size 36 font elsewhere so that EVERYONE can see it, not just biologists.

[Skidous]

Should post that impact size 36 font elsewhere so that EVERYONE can see it, not just biologists.

Yes it should be I just didn't know where that place was

[RuiAce]

Yes it should be I just didn't know where that place was

HSC discussion thread will do lol

Because it applies to every subject and not just science, that's perhaps your best bet.

[AngelicOnyx]

I'm still confused on the phloem part. Is sugar still being moved in step 3? In step 2 the sugars are already actively transported to the areas of the plant where they are needed. Shouldn't the theory end here?

Hmm I'm not excellent at Biology, but isn't the pressure flow theory a continuous process in the plant? Sugar is still being continuously added and removed, which also affects the water pressure

[melprocrastinator]

Hey what did you mean by 'lose marks for things i didnt even know i needed'?

Hey!
For example it would be a four mark question, and 2 of the marks were allocated to an example... but the question never said provide or give an example.
There was also a two marker in trials about "IDENTIFYING" Darwins impact on evolution or something, and i talked about natural selection and survival of the fiitest blah blah blah, yet i only got one mark because i didnt mention his journey/ work with the darwin finches. Like i knew  what that was, but i didnt think it was neccessary for a two mark identify question.
Does that make sense? hahaha

Moderator Action: Moved from the How to Get Band 6 in Biology Thread to Biology Question Thread to make it easier for other forum users to see the question and get the answer as it may assist them in their studies. Thanks for asking the question though

[Skidous]

Hey!
For example it would be a four mark question, and 2 of the marks were allocated to an example... but the question never said provide or give an example.
There was also a two marker in trials about "IDENTIFYING" Darwins impact on evolution or something, and i talked about natural selection and survival of the fiitest blah blah blah, yet i only got one mark because i didnt mention his journey/ work with the darwin finches. Like i knew  what that was, but i didnt think it was neccessary for a two mark identify question.
Does that make sense? hahaha

Hey melprocrastinator
Your questions is sorta hard to understand, do you happen to have a copy of the question or maybe what paper it is from so I can help you out?