© boardworks ltd 2004 1 of 44 ks4 biology movement in and out of cells

© Boardworks Ltd 20041 of 44

KS4 Biology

MovementIn and Out of Cells


Osmosis

Experiments: diffusion and osmosis

Movement In and Out of Cells

Diffusion and life processes

Active transport

Contents

What is diffusion?

Multiple-choice quiz


Why does the colour of concentrated fruit drink change when it is added to water?

Why can you smell cooked food from a distance?

Smells and liquids spreading out

Why can you smell perfume or aftershave when someone walks past you?


These processes are all examples of diffusion.

Smelling cooked food or perfume and diluting juice in water all involve things moving around and spreading out.

Smells and liquids spreading out

Diffusion involves the movement of molecules.What type of molecules are moving in these examples?


The molecules in every substance are always moving.

Moving molecules

In which state are molecules able to spread out?

water (liquid) water vapour (gas)

Diffusion involves the movement of gas and dissolved molecules. Why don’t solid molecules diffuse?

ice (solid)


When smelling body spray where is the smell strongest and where is the smell weakest?

Diffusion and changing concentrations

Smell is strongest at source.

Diffusion means the smell spreads out and gets weaker further away from the source.

How does the concentration of smell molecules change during diffusion?

Smell molecules move from an area of high concentration to an area of lower concentration. This is called a concentration gradient.


Where will the molecules be after diffusion?Diffusion can be represented on a simple diagram.

Changing concentrations

before diffusion

Diffusion is the movement of gas or dissolved molecules from higher to lower concentration.

Molecules diffuse down a concentration gradient.What does this mean?

after diffusion

What has happened to the concentration of the molecules?


Diffusion animation 1


Osmosis




Active transport

Contents

What is diffusion?



Why is diffusion so important?

Diffusion occurs in the organ systems that control your breathing, circulation, digestion and other life processes.

Diffusion explains why you can smell smelly smells and what happens when you dilute a concentrated fruit drink.

More importantly, diffusion is an essential process that is going on inside your body right now and keeping you alive!


Diffusion is the movement of gas or dissolved molecules.

What gas and dissolved molecules do body cells need?

Your body’s survival depends on oxygen and dissolved food molecules getting into your cells.


How do these vital substances cross boundaries within the body to get to where they are needed?

Oxygen and dissolved food molecules must diffuse into and out of the blood for transportation around the body.

Where does diffusion take place within the body?


Breathing involves the exchange of gases in the lungs, a process which occurs by diffusion.

What is the vital gas that you breathe in?

Diffusion and breathing

The lungs have a huge surface area to maximize the exchange of oxygen and carbon dioxide with each breath.

Where in the lungs does gas exchange take place?

oxygen

carbon dioxide

What is the waste gas that you breathe out?


Gas exchange takes place in the alveoli, the tiny air sacs at the end of the bronchioles.

Diffusion and breathing

What are these blood vessels around each alveolus called?


Inhaling increases the concentration of oxygen molecules in an alveolus.

At this point, how does this compare with the concentration of oxygen in deoxygenated blood in the capillary?

Diffusion and breathing – oxygen

deoxygenated blood from the body

oxygenated blood to the body

When you inhale,the concentration of oxygen inside each alveolus ishigher than in deoxygenated

blood.

oxygen into alveoli


How is the concentration of oxygen in the blood increased?

Oxygen molecules diffuse across the lining of the alveolus into the blood in the capillary, moving from higher to lower concentration.

Diffusion and breathing – oxygen



oxygen into alveoli

diffusion When you inhale,the concentration of oxygen inside each alveolus ishigher than in deoxygenated

blood.


Deoxygenated blood from the body is low in oxygenbut has high levels of carbon dioxide.

How does this compare with concentration of carbon dioxide in the alveolus?

Diffusion and breathing – carbon dioxide



The concentration of carbon dioxide in deoxygenated blood is higher

than in deoxygenated

blood.


How is the concentration of carbon dioxide in the blood reduced?

Carbon dioxide molecules diffuse from the blood in the capillary into the alveolus, moving from higher to lower concentration.

Diffusion and breathing – carbon dioxide



The concentration of carbon dioxide in deoxygenated blood is higher

than in deoxygenated

blood.

carbon dioxide out of alveoli

diffusion


Gas exchange animation


Diffusion and digestion

Digestion breaks large food molecules into smaller molecules that can be used by the body.

Dissolved food molecules then need to be transported from the small intestine into the bloodstream.

Where in the small intestine does this diffusion take place?

Carbohydrates, proteins and fat are made up of large molecules that cannot be used directly by the body.


Inside the small intestine


Cross-section of a villus

Each villus separates the digested food in the small intestine from a network of capillaries.


Diffusion from the small intestine

Each villus has a surface layer that is one cell thick.

How does the concentration of dissolved food molecules in the small intestine compare with the blood entering a villus?

The concentration of dissolved food molecules

is higher in the small intestine than in the

blood entering the villus.

wall of small intestine

blood entering villus

blood leaving villus

inside the small intestine


Diffusion from the small intestine

Dissolved food molecules diffuse from the small intestine into the blood, moving from higher to lower concentration.

How is the concentration of dissolved food molecules in the blood increased?

The concentration of dissolved food molecules

is higher in the small intestine than in the

blood entering the villus.

wall of small intestine

blood entering villus

blood leaving villus

inside the small intestine

diffusion


Diffusion in and out of cells

Oxygen and dissolved food molecules are transported to the body’s cells in the bloodstream.

How does the concentration of these useful substances in the blood compare with the concentration inside the cells?

The concentration of oxygen and dissolved

food molecules is higher in the blood

arriving at the cells than inside the cells.



How do oxygen and dissolved food molecules pass from the blood into the cells?

Oxygen and dissolved food molecules diffuse into the body cells, moving from higher to lower concentration.

The concentration of oxygen and dissolved

food molecules is higher in the blood

arriving at the cells than inside the cells.

What process involving these useful substances takes place inside the cell?

diffusion



The cells use the food and oxygen for respiration.

Carbon dioxide is the waste product of respiration and will poison a cell if it is not removed. How is it removed?

Carbon dioxide molecules diffuse from the cells into the bloodstream, moving from higher to lower concentration.

How is this waste carbon dioxide removed from the body?

diffusion


Osmosis




Active transport

Contents

What is diffusion?



What is active transport?

Movement of substances in and out of cells by diffusion involves molecules moving down a concentration gradient from high to low concentration.

Sometimes substances move into cells from low to high concentration. This is called active transport.

Active transport needs energy to make it happen.

How do molecules move along the concentration gradient during active transport?

high concentration

low concentration

diffusion active transport


Active transport and plants

Plants need mineral elements from the soil for healthy growth. Minerals enter a plant though its roots.

The concentration of minerals in the soil is lower than that inside a root hair cell, so how do minerals enter the root cell?

soil

mineralelement

root hair cell


Active transport and plants

Minerals enter a root cell by active transport.

The plant uses energy to move minerals up the concentration gradient from the soil into its root cells.

Why is it important for plants to use energy in this way?

soil

mineralelement

root hair cell

active transport


Osmosis




Active transport

Contents

What is diffusion?



What is osmosis?

Osmosis is a special type of diffusion.

Diffusion involves gas or dissolved molecules, but osmosis only involves the movement of water molecules.

Osmosis occurs across a semipermeable membrane which has tiny holes in it.

These holes are small enough for water molecules to pass

watermolecule

through but larger molecules cannot pass through.


What happens during osmosis?

Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration across a semipermeable membrane.

Osmosis is a type of diffusion, so what do you think happens to water molecules during this process?

watermolecule

semipermeable membrane

osmosis


Osmosis experiment

A bag made from a semipermeable membrane is tied to a glass tube and filled with a strong sugar solution.

What happens to the water molecules in the weak solution?

What happens to the liquid inside the semipermeable bag?

This bag is placed in a weak sugar solution.

strong sugar solution

weak sugar solution


strong sugar solution

weak sugar solution

Osmosis experiment

Water molecules diffuse across the membrane from the weak sugar solution into the strong sugar solution. This continues until the concentration is the same on both

The volume of liquid in the semipermeable bag increases. The liquid rises up the glass tube and then stops. Why does this happen?

sides of the membrane.


Osmosis animation 1


Osmosis animation 2


Osmosis




Active transport

Contents

What is diffusion?



Experiment to demonstrate diffusion


Experiment to investigate osmosis


Osmosis




Active transport

Contents

What is diffusion?


© boardworks ltd 2004 1 of 44 ks4 biology movement in and out of cells

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