MOVEMENT INTO AND OUT OF CELLS

Smells and liquids spreading out Why can you smell cooked food from a distance? Why does the colour of concentrated fruit drink change when it is added to water? Why can you smell perfume or aftershave when someone walks past you?

Smells and liquids spreading out Smelling cooked food or perfume and diluting juice in water all involve things moving around and spreading out. These processes are all examples of diffusion. Diffusion involves the movement of molecules. What type of molecules are moving in these examples?

Moving molecules ice (solid) water (liquid) water vapour (gas) The molecules in every substance are always moving. In which state are molecules able to spread out? ice (solid) water (liquid) water vapour (gas) Diffusion involves the movement of gas and dissolved molecules. Why don’t solid molecules diffuse?

Diffusion and changing concentrations When smelling body spray where is the smell strongest and where is the smell weakest? Diffusion means the smell spreads out and gets weaker further away from the source. Smell is strongest at 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.

Changing concentrations Diffusion can be represented on a simple diagram. Where will the molecules be after diffusion? before diffusion after diffusion What has happened to the concentration of the molecules? Diffusion is the movement of gas or dissolved molecules from higher to lower concentration. Molecules diffuse down a concentration gradient. What does this mean?

Diffusion animation 1

Diffusion animation 2

Diffusion animation 3

Why is diffusion so important? 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 occurs in the organ systems that control your breathing, circulation, digestion and other life processes.

Diffusion and life processes 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?

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.

Diffusion in and out of 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. diffusion What process involving these useful substances takes place inside the cell?

Diffusion in and out of cells 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? diffusion 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?

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. high concentration diffusion active transport 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?

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? root hair cell mineral element soil

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? active transport root hair cell mineral element soil

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. water molecule Osmosis occurs across a semipermeable membrane which has tiny holes in it. These holes are small enough for water molecules to pass through but larger molecules cannot pass through.

What happens during osmosis? Osmosis is a type of diffusion, so what do you think happens to water molecules during this process? osmosis water molecule semipermeable membrane 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 experiment A bag made from a semipermeable membrane is tied to a glass tube and filled with a strong sugar solution. This bag is placed in a weak sugar solution. strong sugar solution weak sugar solution What happens to the water molecules in the weak solution? What happens to the liquid inside the semipermeable bag?

Osmosis experiment The volume of liquid in the semipermeable bag increases. The liquid rises up the glass tube and then stops. Why does this happen? strong sugar solution weak sugar solution 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 sides of the membrane.

Osmosis animation 1

Osmosis animation 2

Experiment to demonstrate diffusion

Experiment to investigate osmosis