Movement of substances around the body

Question 1

Why is it important?

Answer 1

• vital to maintain homeostasis
• Nutrients need to enter cells, waste products need to leave them.
• Hormones need to send chemical messages.
• Water needs to maintain a stable distribution throughout the body.

Question 2

What are passive forms of transport?

Answer 2

• No energy required.
• Involve movement down a concentration gradient, ie from an area of high concentration to an area of low concentration to even things up.
• Diffusion – movement of a chemical from an area of high concentration to low concentration - can be gases, liquids or solutions. May be facilitated.
• Osmosis – involves the movement of water molecules from a high concentration to a low concentration across a semi-permeable membrane. The force required to do this is called osmotic pressure.

Question 3

What is facilitated diffusion?

Answer 3

• the passive movement of molecules along the concentration gradient.
• selective process, i.e., the membrane allows only selective molecules and ions to pass through it.
• prevents other molecules from passing through the membrane.
• Allows molecules that are unable to freely cross the phospholipid bilayer (e.g. large molecules such as glucose) .
• Involves two distinct types of transport proteins – channel proteins and carrier proteins. Carrier proteins can be active or passive depending on the concentration gradient.

Question 4

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What does a carrier protein do?

Answer 4

Binds to a special molecule which changes its structure and allows molecules through.

Question 5

What does a protein channel do?

Answer 5

Selectively allow certain substances to pass through the cell membrane

Question 6

What is osmotic pressure?

Answer 6

• The pressure required to stop water from diffusing through a barrier by osmosis ie how hard the water would “push” to get through the barrier in order to diffuse to the other side.
• Determined by solute concentration – water will “try harder” to diffuse into an area with a high concentration of a solute, such as a salt, than into an area with a low concentration.

Question 7

Define the term hypertonic.

Answer 7

the osmotic pressure of the solution outside the cells is higher than the osmotic pressure inside the cells. The water inside the cells exits in an attempt to equalize the osmotic pressure, causing the cells to shrink.

Question 8

Define the term Hypotonic.

Answer 8

The solution outside of the cell has a lower osmotic pressure than the inside of the cell - the solution is hypotonic with respect to the cells. The cells take in water in an attempt to equalize the osmotic pressure, causing them to swell and potentially burst.

Question 9

Define the term Isotonic

Answer 9

The osmotic pressure outside the cell is the same as the pressure inside the cells, the solution is isotonic with respect to the cytoplasm. This is the usual condition of red blood cells in plasma.

Question 10

What is the link between albium and osmotic pressure?

Answer 10

• protein found in blood plasma. Helps maintain the osmotic pressure between the blood vessels and tissues. Serum albumin accounts for 55 percent of the total protein in blood plasma.
• Enters the bloodstream and helps keep fluid from leaking out of your blood vessels into other tissues. It is also carries hormones, vitamins, and enzymes throughout your body.
• Low albumin levels can lead to fluid leaking out of the blood and building up in the lungs, abdomen and other body parts.

Question 11

Give an example of a clinical application for this.

Answer 11

• Ascites – fluid collects in the abdominal spaces. The pressure from this impacts on the function of the lungs, kidneys and other organs.
• Causes abdominal pain, swelling, nausea, vomiting and many other problems. The abdomen may have to be regularly drained in hospital.
• Can be caused by chronic alcoholism (severe liver disease – cirrhosis)

Question 12

What is active transport?

Answer 12

• Transport of substances up the concentration gradient (from lower to higher concentration).
• Requires ATP
• Facilitated transport – carrier molecules made of protein transport substances into or out of the cell. This is active transport if the movement is from an area of low concentration to high concentration.
• These sites are highly specialised and can be used only by one particular substance, which can affect the speed at which this system can operate.

Question 13

What is the sodium potassium pump?

Answer 13

• Maintains the homeostasis of sodium (extracellular electrolyte) and potassium (intracellular electrolyte)
• Pumps sodium out of the cell, where its concentrations are usually lower, to the higher concentrations of sodium outside the cell, and potassium back into the cell, again to an area of higher concentration.
• Huge energy requirement – big consumer of ATP.
• The sodium potassium pump plays an important role in contraction of the heart muscle, as well as kidney function and nerve signalling (action potential)