IGCSE BIOLOGY DOUBTS HERE !!!!

[elemis]

Before posting your IGCSE Biology doubts here, have a look in this thread.

Use the search function in that thread to see if your doubt has already been answered.

If it hasn't then post here and someone will help you.

Don't forget to mention the following ;

1. The Year and session.
2. The Question number/part you have doubt in.

It would be better if you uploaded the paper by attaching it.

Check THIS for Resources =D

Thank you =)

[WARRIOR]

Hello !

Can someone be kind enough to answer this silly question.

What is the difference between Prokaryotes and Protoctista?

[nid404]

Prokaryotes lack a nucleus.

 protocists are eukaryotic, so it consists of a nucleus.

[WARRIOR]

Prokaryotes lack a nucleus.

 protocists are eukaryotic, so it consists of a nucleus.

all right , cheers thanks!

[WARRIOR]

Greetings !

 I have a question ,

In my book the drawing of a normal animal cell is different to a 'liver cell' , i can see that liver cell has the following extra:
Ribosomes on endoplasmic reticulum
a 10x bigger mitochondria!!

should i mark the difference? so when i come to draw a liver cell should you add those 2?

thx in advance !

[The Golden Girl =D]

Greetings !

 I have a question ,

In my book the drawing of a normal animal cell is different to a 'liver cell' , i can see that liver cell has the following extra:
Ribosomes on endoplasmic reticulum
a 10x bigger mitochondria!!

should i mark the difference? so when i come to draw a liver cell should you add those 2?

thx in advance !

Well for me i solved almost all the pps for Bio ..and that wasn't there ....so believe it's negligible   srry what i meant is just forget it

[Deadly_king]

Nope.......no need to mark these differences. They are negligible. Ribosomes found on the endoplasmic reticulum is known as rough E.R and it may occur in any animal cell.

Moreover the size of the mitochondria does not mean anything except that perhaps it carries out much respiration. However these are not considered as differences

[WARRIOR]

• Describe the importance of diffusion of gases
and solutes and of water as a solvent

THX

[Deadly_king]

• Describe the importance of diffusion of gases
and solutes and of water as a solvent

THX

Importance of diffusion of gases :
Carbon dioxide and Oxygen diffuse in and out of leaves. They are required for both respiration and photosynthesis (the two most important processes for life to occur).

Diffusion of solutes :
Transport of materials. Water or the solution acts as transport medium. Example : blood

Water as a solvent :
1. This is important as it allows ions and polar molecules to move freely within itself. Some specific ions are essential for survival of plants (e.g). They dissolve in water to get it specific cells.
 2. Oxygen and carbon dioxide diffuse within a layer of moisture around mesophyll cells in order to get in. It facilitates diffusion.
Again water acts as a transport medium.

Hope it helps

[Vin]

Thanks a lot King. Do you mind if I add exactly same stuff to the bunch of bio notes?

[WARRIOR]

Importance of diffusion of gases :
Carbon dioxide and Oxygen diffuse in and out of leaves. They are required for both respiration and photosynthesis (the two most important processes for life to occur).

Diffusion of solutes :
Transport of materials. Water or the solution acts as transport medium. Example : blood

Water as a solvent :
1. This is important as it allows ions and polar molecules to move freely within itself. Some specific ions are essential for survival of plants (e.g). They dissolve in water to get it specific cells.
 2. Oxygen and carbon dioxide diffuse within a layer of moisture around mesophyll cells in order to get in. It facilitates diffusion.

Hope it helps
Again water acts as a transport medium.

+ rep thx!

[Deadly_king]

Thanks a lot King. Do you mind if I add exactly same stuff to the bunch of bio notes?

Not at all Vin. Am just glad being able to help

You're welcome guys

[acash09]

Hey guys, can someone explain to me the meaning of negative feedback? Its in the homeostasis lesson about the hypothalamus.
Is it needed in any other lesson for the 2010 exams?

Much appreciated.
Acash09

[nid404]

Hey guys, can someone explain to me the meaning of negative feedback? Its in the homeostasis lesson about the hypothalamus.
Is it needed in any other lesson for the 2010 exams?

Much appreciated.
Acash09

This is a small part of the syllabus and I've hardly come across any questions when I was doing my igz but you need to know what negative feedback is.

Homeostasis is the maintenance of constant internal conditions. It is often controlled be negative feedback There are six different things which need to be kept constant
Removal of carbon dioxide
Removal of urea
(Of these two we don’t need any of them, they are constantly being produced by the body and we need to constantly get rid of them.)
Ion content
Water Content
Sugar content
Temperature
Amount of thyroxin
(We need these four in certain amounts, and too much can be dangerous.)

The hypothalamus (or thermoregulatory gland) is located just above the pituitary gland. It contains sensors which monitor blood temperature and water content, and send nerve impulses to the pituitary gland. It also monitors carbon dioxide which is removed by the lungs in exhaled air. The kidneys control water content (via ADH) and ion content of the blood. The pituitary gland produces ADH for the kidneys, while the skin helps control the body temperature by sweating and raising hairs. The muscles can shiver to increase temperature. Finally the liver and pancreas work together to keep the blood sugar levels correct.

The pituitary gland secrets thyroid stimulating hormone, and the more secreted the more thyroxin is made. However, if too much thyroxin is made then it goes back to the pituitary gland and tells it to stop making so much thyroid stimulating hormone.<< when there is excess of a certain hormone, the hormone acts as an inhibitor in itself and stops its own production..This is negative feedback.

[MKL]

This is a small part of the syllabus and I've hardly come across any questions when I was doing my igz but you need to know what negative feedback is.

Homeostasis is the maintenance of constant internal conditions. It is often controlled be negative feedback There are six different things which need to be kept constant
Removal of carbon dioxide
Removal of urea
(Of these two we don’t need any of them, they are constantly being produced by the body and we need to constantly get rid of them.)
Ion content
Water Content
Sugar content
Temperature
Amount of thyroxin
(We need these four in certain amounts, and too much can be dangerous.)

The hypothalamus (or thermoregulatory gland) is located just above the pituitary gland. It contains sensors which monitor blood temperature and water content, and send nerve impulses to the pituitary gland. It also monitors carbon dioxide which is removed by the lungs in exhaled air. The kidneys control water content (via ADH) and ion content of the blood. The pituitary gland produces ADH for the kidneys, while the skin helps control the body temperature by sweating and raising hairs. The muscles can shiver to increase temperature. Finally the liver and pancreas work together to keep the blood sugar levels correct.

The pituitary gland secrets thyroid stimulating hormone, and the more secreted the more thyroxin is made. However, if too much thyroxin is made then it goes back to the pituitary gland and tells it to stop making so much thyroid stimulating hormone.<< when there is excess of a certain hormone, the hormone acts as an inhibitor in itself and stops its own production..This is negative feedback.

You need to be able to describe the function of the kidney in removing urea/excess water for Core, and need to be able to outline the structure of the kidney and structure + functioning of the nephron for Supplement, including the role of the renal capsule and the tubule.

Only negative feedback loops for maintenance of temperature in skin (Core) and maintenance of glucose content via insulin/glucagon (Supplement) are needed for IGCSE. At least that's what it says on the 2010 Syllabus.