Diffusion, Osmosis, And Active Transport

Question 1

What is diffusion

Answer 1

• diffusion ids the spreading out of particles from an area of higher concentration to an area of lower concentration

Question 2

Where does diffusion happen

Answer 2

Diffusion happens in solutions and gases - because the particles are free to move

Question 3

What is the simplest type of diffusion

Answer 3

• when different gases diffuse through each other.
• This is what’s happening when the smell of perfume diffuses through a room

Question 4

What effects the rate of diffusion

Answer 4

• the bigger the concentration gradient (the difference in concentration), the faster the diffusion rates
• A higher temp will also give a faster diffusion rate because the particles have more energy so move around faster
• The larger these surface area of the membrane, the faster the diffusion rate - more particles can pass through at once

Question 5

Explain how cell membranes work with diffusion

Answer 5

• dissolved substances can move in and out of cells by diffusion
• Only very small molecules can diffuse through cell membranes (such as oxygen, glucose, amino acids and water)
• Big molecules like starch and proteins can’t fir through these membranes

Question 6

What is osmosis

Answer 6

The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower concentration

Question 7

What is a partially permeable membrane

Answer 7

A partially permeable membrane is one with very small holes, so small that only tiny molecules (like water) can pass through them

Question 8

Which way do the water molecules pass through during osmosis

Answer 8

• both ways through the membrane because water molecules move about randomly all the time

Question 9

What us the net movement of water molecules

Answer 9

• remember that there are more water molecules on one side than the other, there’s a steady net flow of water into the region with fewer water molecules
• i.e. into the stronger sugar solution
• This means that the strong sugar solution gets more dilute. The water acts like it’s trying to “even up” the concentration either side of the membrane
• Osmosis is a type of diffusion - passive movement of water particles from an area of high water concentration to an area of lower water concentration

Question 10

Describe an experiment to observe osmosis

Answer 10

• cut up potato into identical cylinders
• get beakers with different sugar solutions in them
• one should be pure water and another should be a very concentrated sugar solution
• then have others with concentrations in between
• measure mass of cylinder, then leave one cylinder in each beaker for 20 hours or so
• then you take them out, dry them with a paper towel and measure their masses again
• if the cylinders have drawn in water by osmosis, they’ll have increases in mass
• if water has been drawn out, they’ll have decreased in mass
• you can calculate % change in mass, then plot a graph

Question 11

What is the independent and dependent and control variable in the osmosis experiment

Answer 11

• dependant variable = chip mass
• independent variable = concentration of sugar solution
• control = volume of solution, temp, time, type of sugar used

Question 12

What are some errors that might arise in the osmosis experiment and how do you reduce them

Answer 12

• some potato chips aren’t fully dried, this would hive a higher mass
• if water evaporated from the beakers, the concentrations of the sugar solutions would change
• you can reduce the effects of these errors by repeating the experiment and calculating a mean % change at each concentration

Question 13

How do Root Hair cells take in Minerals and water

Answer 13

• they use their microscopic hairs which give its a larger SA for absorbing water and mineral ions from soil for healthy growth
• The concentration of minerals is usually higher in the root hair cells than in the soil around them. So the root hair cells can’t use diffusion to take up minerals from the soil
• they use active transport instead
• it allows them to absorb minerals from a very dilute solution, against a concentration gradient
• This is essential for growth
• But active transport needs energy from respiration to work

Question 14

Where for humans does active transport happen

Answer 14

• Taking in glucose from the gut and from the kidney tubules
• It is done in the gut where there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood
• When there’s a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood
• BUT - sometimes there’s a lower concentration of nutrients in the gut than there is in the blood
• this means that the concentration gradient is the wrong way
• The same process used in plant roots is used here — Active transport
• Active transport allow nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way
• This means that glucose can be take into the bloodstream when its concentration in the blood is already higher than in the gut. It can then be transported to cells, where it’s used for respiration