Movement of Substances across Boundaries

Name the processs in which gases move in and out of the cell

Diffusion

What is diffusion?

Diffusion is the net movement of particles (ions or molecules) from an area of high concentration to an area of low concentration gradient.

In a longer thinner bag would diffusion be faster or in a short fat bag?

In a longer thinner bag because it has a larger surface area and diffusion is larger when there is a larger surface area.

What is a crenated cell?

It is a RBC placed in a concentrated solution loses water + cell contents reduced in volume. The cytoplasm becomes more viscous and therefore harder for substances to move through

What is a Haemolysed cell?

It is a RBC placed in a dilute solution it then gains water it also gains volume and then bursts. The volume increase and puts pressure on the cell membrane it bursts and throws out the content of the cell. It's useless

What is osmosis?

It is the diffusion of water through a partially permeable membrane. It moves from an area of high concentration to low.

How would you tell if active uptake was taking place?

It moves from an area of low concentration to an area of high concentration

What is a normal cell during osmosis?

It should be places in a solution which has a equal concentration to itself. This is its optimum conditions for working. The plasma should have the same concentration as the inside of the RBC.

Four facts about active transport

It's against a concentration gradient Very fast Energy is needed in the form of ATP. Produced by respiration and therefore oxygen is needed. Special carrier proteins are used to take the molecules across the membrane e.g. minerals into root hairs of plants glucose from the small intestine into the blood

A cook prepares fresh fruit salad after two hours it's surrounded by syrup why?

Osmosis occurred. Higher concentration of water in the fruit the water particles moved out of the fruit into the sugar . In osmosis water molecules move from an area of high concentration to low. The sugar dissolved in the water and therefore turned into a syrup

Answer True or False Diffusion takes place in all substances Diffusion is usually quicker in liquids than gases Diffusion happens faster when there is a higher concentration gradient A large surface area makes diffusion happen more quickly When there is a larger distance this speeds up the rate of diffusion

TRUE FALSE TRUE TRUE FALSE

What factors can affect the rate of diffusion?

Temperature Medium it's passing through Concentration gradient

Students placed 4 potato cylinders in different conc. of sodium chloride. Name one variable would need to control in the experiment and how it could be achieved

The amount of time the cylinder put into the solution they could police this by using a stopwatch and a set time

What is incipient plasmolysis?

The cell memebrane is just starting to pull away from the cell wall.

In a tube there is glucose and starch solution outside is water what would be outside the bag and why?

The glucose would be outside the bag because the molecules are small enough to diffuse through the plastic

What happens in the experiment with the starch solution and the dilute iodine solution? (5 marks)

The starch solution is on the inside of the visking tube while the iodine solution is out. The iodine will diffuse through the visking tube because it moves from a level of high concentration to low. The starch molecules stay in the visking tube because the starch molecules are too big to diffuse through the bag. The visking tube is semi permeable it only lets certain things in and out of it. This is similar to the cell membrane.

If there was agar and dye in a test tube with decreasing amount of dye in each what would happen?

The tube with the most dye will diffuse the fastest because there's a higher concentration gradient between the dye and agar leading to a steep gradient and faster diffusion

What happens when a plant cell is put in a concentrated solution?

The vacuole decreases in volume. The cell is therefore not full and therefore no support given and the plant wilts. The cells are then Flaccid. It loses water and becomes plasmolysed.

What happens when a plant cell is put in a dilute solution?

The vacuole fills up and increase in volume . It exerts pressure on the cytoplasm it pushes against the cell wall. The wall pushes back and when no more water can enter the cell is said to turgid. A turgid cell supports the plant cell

What happens if a visking tube is filled with a 20% sugar solution and on the outside is distilled water?

The volume of the bad would increase as there is a higher concentration of water molecules outside of the bag and the particles move from an area of higher concentration to an area of low concentration.

Describe a method you would use to ensure the cylinders are cut to the same length

Use a ruler and then cut it with a knife and compare it to the other cylinders

Explain how concentration affects the rate of diffusion

a) A big difference in concentration leads to a steep slope then a steep gradient= FAST DIFFUSION b) A small difference leads to a small slope , a small gradient = SLOW DIFFUSION

Complete sentence a) An example of diffusion in the lung of a mammal involves a substance called oxygen which moves from the ----------------- to the -------------------- b) An example of osmosis in the kidney of a mammal involves a substance called ---------- which moves from the nephron to the ----------- c) An example of active transport in a flowering plant involves uptake of a mineral salt , which moves from the ----------- to the ---------- in a root hair cell

alveoli, bloodstream water, blood soil

What are the three methods for the movement of substances across boundaries?

1. Diffusion 2.Active transport/ uptake 3. Osmosis (water only)

Explain the factors which effect the rate of diffusion?

1. Temp.- The higher the temperature the particles gain more kinetic energy so rate of diffusion= faster 2. Medium - It's easier to pass through a gas because the particles are more spread out so it's easier pass through than a solid or liquid. 3. Concentration gradient- The difference between the two areas.