UNIT 5 BIOLOGY B4 (ORGANS & SYSTEMS)

Describe the parts of the phospholipid bilayer

• HYDROPHILIC phosphate head which is POLAR

• HYDROPHOBIC fatty acid tails which is NON-POLAR

What does it mean by the terms “polar” and “non-polar”?, give examples of the parts of the phospholipid bilayer that are polar and non-polar.

• Polar = attracted to water, such as the hydrophilic phosphate heads

• Non-polar = repelled by water, such as the hydrophobic fatty acid tails

State the two main features of the fluid mosaic model

• Fluid Part- Phospholipids and proteins can move laterally (side to side)

• Mosaic Part- Refers to how the phospholipid bilayer is embedded with different proteins

State the three roles of cholesterol in cell surface membranes

• Cholesterol adds mechanical stability

• Cholesterol increases rigidity

• Cholesterol prevents the loss of ions

Describe what a glycoprotein is and state the two main roles of glycoproteins in cell surface membranes

• Glycoproteins are carbohydrates covalently bonded to proteins,

• Function 1 - they act as receptors for hormones

• Function 2 - acts as antigens which allows cells to recognise each other as “self”

Describe what a glycolipid is and state the two main roles of glycolipids in cell surface membranes

• Glycolipids are carbohydrates covalently bonded to a phospholipid

• Function 1 - act as receptors for hormones

• Function 2 - acts as antigens which allows cells to recognise each other as “self”

Describe what a channel protein is and explain its role in the phospholipid bilayer

• Intrinsic (go across the whole bilayer) proteins that have a channel lined with hydrophilic amino acids

• They allow the transport of ions and polar molecules DOWN their concentration gradient.

Describe what a carrier protein is and explain its role in the phospholipid bilayer

• Intrinsic proteins that have a pocket lined with hydrophilic amino acids.

• They allow the transport of ions and polar molecules DOWN and AGAINST their concentration gradient, by changing shape

Describe what extrinsic proteins are and state the two main roles of extrinsic proteins in cell surface membranes

• Unlike intrinsic proteins, extrinsic proteins are only found on one side of the cell membrane

• Their functions include: Membrane bound enzymes & acting as antigens

Give one similarity and one difference between a channel protein and a carrier protein

Carrier Proteins:

• Changes shape & moves substances against their conc gradient

Both:

• Transport ions

• Go through the whole phospholipid bilayer

What is a Red blood cell, Phagocyte & Squamous endothelium of blood capillary

• Red blood cell - Main cellular component of blood and moves around at extremely high speeds & pressures

• Phagocyte - A type of white blood cell that regularly changes shape and can fit through small pores in capillaries

• SE - Makes up blood vessels called capillaries & are continuous hit by red blood cells which move at high speeds

1. Why do phagocytes have a low percentage cholesterol?

2. Why do red blood cells need more cholesterol than phagocytes?

3. Why do SE have a very high amount of cholesterol in their membrane?

1. They have to be flexible to move through small pores & capillaries, and carry out phagocytosis

2. They move at high speeds and pressure through the circulatory system, so need rigidity to keep their biconcave shape

3. They are continuously hit by RBC that move at high speed and pressure so need a lot of mechanical stability to prevent damage.

1. What is simple diffusion?

2. Both simple and facilitated diffusion is a passive process, what does this mean?

1. Net movement of small non polar particles from an area of a high conc to low conc, down their conc gradient. This is a passive process where these substances move between phospholipids.

2. Diffusion does not require any metabolic energy

1. What is facilitated diffusion?

2. What is a polar molecule?

1. Net movement of polar particles from a high to low conc, down their conc gradient. This is a passive process where these substances move between channel or carrier proteins.

2. Covalent molecules with an unequal distribution of electrons.

Describe some similarities & differences between facilitated diffusion and simple diffusion

• Both are passive processes (doesn’t require additional energy)

• Both move substances down their conc gradient, from a high to low conc

• FD moves polar substances + ions through intrinsic protein, whereas SD moves small non polar, lipid soluble substances between phospholipids.

Explain why small, uncharged, lipid soluble molecules can go through without the use of a protein

• They are non-polar and so are hydrophobic

• Therefore, they will not be repelled by the hydrophobic fatty acid centre of the bilayer

Describe what is meant by the phrase ‘lipid soluble’ and explain why the lipid soluble molecules can go through without the use of a protein

• It means dissolves in lipids

• Therefore, lipid soluble molecules are non-polar and so are hydrophobic and will not be repelled by the hydrophobic fatty acid tail

1. Give an example of a lipid soluble molecule

2. Name two intrinsic proteins involved in facilitated diffusion

1. Oxygen and steroid hormones

2. Channel and carrier proteins

Channel proteins transport molecules such as ions ( e.g. Na+). Channel proteins work in a specific way, explain what this means

It only changes shape for one chemical/ion

Explain how carrier proteins work

• Carrier proteins are specific, so they have a binding site for only on type of ion lined with hydrophilic amino acids.

• When the ion binds, the carrier protein changes shape, and transports the ions to the other side

State the chemical formula of glucose and suggest why it is unable to fit through gaps between phospholipids in the phospholipid bilayer- (simple diffusion)

Glucose = C6 H12 O6 (24 atoms)

• It is unable to fit through gaps between phospholipids in the phospholipid bilayer because it is too large and it is polar

What is active transport?

• Movement of molecules against their conc gradient, through intrinsic carrier proteins

• This process requires ATP/energy.

• Charged, polar molecules (e.g glucose, ions) travel this way.

How is active transport different to diffusion?

• Active transport requires ATP, whereas diffusion does not.

• Active transport only uses carrier proteins, whereas diffusion uses channel and carrier proteins, or none in simple diffusion.

What is ATP and how does it give us energy?

• ATP is a molecule produced by the process of respiration

• ATP stores chemical energy in chemical bonds. When the chemical bonds are broken, this releases energy

In active transport, what is the energy needed to do?

ATP is needed to change the shape of the carrier protein

Define Osmosis

• Movement of water molecules from a high to low conc, down their conc gradient

• This is across a partially permeable membrane

1. What is a solute?

2. What does the addition of solute do to the concentration of water?

1. A substance that dissolves in a solvent

2. Adding a solute to water lowers the water concentration

1. A high water concentration means there is ? solute concentration

2. A low water concentration means there is ? solute concentration

1. low

2. high

Why can water move across the membrane?

• It can move across the phospholipid bilayer as it is small

• it can then move between the phospholipids

Suggest why the steroid hormone can diffuse across the membrane easily

• They are hydrophobic

• So, are not repelled by fatty acid tails which allows them to easily pass through

Suggest why oxygen and carbon dioxide can diffuse across the membrane easily

• o2 molecules are non polar, so they are hydrophobic

• They are not repelled by the hydrophobic fatty acid core of the phospholipid bilayer

1. Which one of the red blood cells was placed in water?

2. Why would a eukaryotic plant cell not burst when it is placed in water?

1. Third picture - water is moved into cells by osmosis, across a semi permeable membrane from a high to low water concentration

2. Because they have a cell wall

What is exocytosis? (also known as bulk transport)

• Vesicles containing large particles like protein, fuse with the cell surface membrane & are transported OUT of the cell

• Requires ATP

• (Examples would be- antibodies and hormones)

What is endocytosis? (also known as bulk transport)

• Vesicles containing large particles like protein, fuse with the cell surface membrane & are transported INTO the cell

• Requires ATP

• (Examples would be- antibodies and hormones)

What happens to the SA:VOL RATIO

• As the size of an object increases the SA:VOL ratio decreases

Calculate the SA, VOLUME AND SA:VOL RATIO for the following:

1. 1cm x 1cm x 1cm

2. 2cm x 2cm x 2cm

3. 3cm x 3cm x 3cm

4. 4cm x 4cm x 4cm

What do you notice as the cube gets bigger?

• Surface area increases

• Volume increases

• However the SA:VOL RATIO decreases

What happens to the SA:VOL ratio, rate of heat loss and rate of diffusion of a small animal?

• SA:VOL ratio is large

• Rate of heat loss is fast

• Rate of diffusion is fast

What happens to the SA:VOL ratio, rate of heat loss and rate of diffusion of a large animal?

• SA:VOL ratio is small

• Rate of heat loss is slow

• Rate of diffusion is slow

1. What is a multicellular organism?

2. Mammals are multicellular organisms. Why do they not exchange gases such as oxygen across their surface?

1. Made up multiple cells

2. Their SA:VR is small, in comparison to single celled organisms, so diffusion is slow