OCR AS Biology (F211) - Jan 2013.

Water enters a cell through osmosis - the diffusion of water from an area of higher water potential to an area of lower water potential, through a partially permeable membrane.

Glucose may enter a cell through facilitated diffusion, and active transport .

Glucose cannot diffuse through the cell surface membrane, as it is too large a molecule.
Facilitated diffusion involves the use of two proteins - channel proteins, and carrier proteins, which are found embedded within the phospholipid bilayer.
Glucose is transported across the membrane using a carrier protein. The glucose molecule attaches to a binding site, found on the surface of the carrier protein. The carrier protein then changes shape, and releases the glucose molecule onto the other side of the membrane - into the cell. In active transport - the movement of molecules against the concentration gradient - these carrier proteins are used as pumps. Using energy released from ATP, the carrier protein move molecules across the membrane at a faster rate than diffusion.

Like osmosis, facilitated diffusion is a passive process. However, the difference between the two transportation techniques is that osmosis only ever refers to the movement of water across a partially permeable membrane from an area of high water potential to an area of lower water potential. Facilitated diffusion is used only for molecules which are too large to diffuse across the cell surface membrane through diffusion.


Question:
(Anyone can answer it if they want! )
Describe and explain the structure of mitochondria.
Hint: I'm talking about the internal structure of the organelle, as well as the outer structure.

Great answers mate! However, I find it necessary to add a bit more to your answer on 'how water enters the cells'. For water to enter the cell (by osmosis), it has to cross the lipid bilayer of the cell membrane. So my answer for that question would be something along this line: water enters the cell by osmosis- the movement of water molecules from a region of higher water potential to a region of lower water potential down a water potential gradient across a partially permeable membrane. Water cross the lipid bilayer of the cell membrane, the membrane contains protein which provide an aqueous channel through which water can pass.

I hope this helps

Thanks!
Looking at the specification REALLY helps. It tells you literally everything you need to know. If it's not in the spec, it's not going to come up in the paper.

I'm not sure whether the extra bit you added is in the spec, but it's most probably worth knowing for the future!


P.S. Instead of diffusion, in my answer, I intended, at that time, to write movement, but I must have been thinking about diffusion at the time.
Make sure to specifically mention 'movement'! Saying it is the diffusion of water may lose you marks! Better to be safe than sorry!

Even better when referring to osmosis is the "net movement".

Thanks!
Looking at the specification REALLY helps. It tells you literally everything you need to know. If it's not in the spec, it's not going to come up in the paper.

I'm not sure whether the extra bit you added is in the spec, but it's most probably worth knowing for the future!


P.S. Instead of diffusion, in my answer, I intended, at that time, to write movement, but I must have been thinking about diffusion at the time.
Make sure to specifically mention 'movement'! Saying it is the diffusion of water may lose you marks! Better to be safe than sorry!

Does anyone know how to calculate heart rate in beats per min? thanks!

More questions.. Yayyy
Umm

Explain how the changes in pressur are brought about during inspiration and expiration?
Inspiration (3marks)
Expiration (3marks)

Personally i found these questions tricky so im comparing answers more then anything

Where can i find the right specification?

Respiratory movements are controlled by nerve impulses from the respiratory control centre in the medulla oblongata of the brain.

During inhalation, the diaphragm contracts, and flattens - pushing down on the digestive organs. The external intercoastal muscles contract, and the internal intercostal muscles relax. The ribs are raised. The volume of the lungs increases, and pressure of the lungs decreases below atmospheric pressure. Air is brought into the lungs through the nose and mouth.

During exhalation, the diaphragm relaxes -it becomes domed shape, as the digestive organs push on it. The external intercostal muscles relax, and the internal intercostal muscles contract. The ribs fall. The volume of the lungs decreases. Pressure rises above atmospheric pressure. Air is brought into the lungs through the nose and mouth.

Does anyone know how to calculate heart rate in beats per min? thanks!

Using the mammalian gaseous exchange system as an example, explain how the different cells and tissues enable the effective exchange of gases ? (5 Marks)

Need help with this question. 5 bullet points please.

I would talk about the squamous epithelium cells in the alveoli of human lungs:-

They're usually one cell thick (the alveoli), thin diffusion barrier and a small distance for substances to diffuse across. At the same time in groups this builds up to have a high surface area to volume ratio.

They're usually coated in a surfactant such as tissue fluid in most cases, hence providing a diffusion medium for substances.

Because it asks you to reference to the human body, you would probably get a mark for correctly referencing an appropriate tissue.

Using the mammalian gaseous exchange system as an example, explain how the different cells and tissues enable the effective exchange of gases ? (5 Marks)

Need help with this question. 5 bullet points please.

anyone who wants to revise?

Why is the muscle mass greater on the left hand side of the heart than the right?