Movement across cells Learning objectives Understand the three

Movement across cells Learning objectives: • Understand the three methods of movement of substances into and out of cells • Understand the importance of osmosis in plants • Understand the factors that affect the rate of movement of substances into and out of cells. Task 1: Answer these following questions: 1. Which substances does a cell need and why? 2. Which part of the cell controls the movement of these substances?

Movement across cells There are three main ways that molecules can pass through the membrane: • diffusion • osmosis • active transport

Deodorant Task: I am going to spray some deodorant in the corner of the room As soon as you can smell it stand up You have 2 min as a group to explain what just happened!

Diffusion Movement of particles from a region of high concentration to a region of low concentration. It is a passive process ; no energy required since it goes with the concentration gradient.

Diffusion: importance All living cells rely on diffusion to live. Task: How is diffusion used by living cells?

Diffusion: importance 1. Getting raw materials for respiration (dissolved substances and gases) Where has the glucose come from? Diffused into blood stream from small intestines Glucose Oxygen Where has the oxygen come from? Diffused into blood stream from alveoli (lungs)

Diffusion: importance 2. Removing waste products (e. g. from respiration) How is the carbon dioxide excreted from the body? Diffuses into alveoli (lungs) and is exhaled

Diffusion: importance 3. Photosynthesis in plants (raw materials in, waste products out) • Carbon dioxide diffuses in through the stomata • Oxygen and water diffuses out of the stomata

Which is ‘more concentrated’? But what does that mean? The more concentrated one has more solute, compared to the volume of water.

Chemistry recap Solute (solid) + solvent (liquid) solution

Osmosis is a special case of diffusion. It is the movement of water from a high water concentration (dilute solution) to a low water concentration (concentrated solution) through a partially permeable membrane. Key: High Water Concentration. Few molecules of solute. Dilute solution Low Water Concentration. Many molecules of solute. Concentrated solution Water molecule Solute molecule Water movement

Osmosis: importance Task 5: Using the picture as a clue, explain why osmosis is particularly important in plants. Watered Unwatered

Osmosis: importance Osmosis is important for plant support. Inside the plant, water moves from cell to cell by osmosis. A plant cell that has a high water concentration in its external surroundings will absorb water by osmosis. The vacuole will swell and push against the cell wall, and the plant will be supported. The cell is said to be turgid.

Osmosis: importance A plant cell that has a low water concentration in its external surroundings will lose water by osmosis. The vacuole will shrink and the pressure on the cell wall decreases. The plant will be unsupported and start to wilt. The cell is said to be flaccid. If this continues the cell membrane and cytoplasm will detach from the cell wall. In this condition, the cell is said to be plasmolysed.

Factors that affect diffusion (and osmosis) include: -Temperature - Diffusion distance (distance the molecules have to travel) - Concentration gradient - Surface area to volume ratio is increased

Factors that affect diffusion (and osmosis) As temperature increases, the rate of diffusion increases. This is because as temperature increases, particles gain more kinetic energy and therefore move faster. Cold Hot water

Factors that affect diffusion (and osmosis) As the distance increases, the rate of diffusion decreases. This is because as distance increases, particles have further to travel.

Factors that affect diffusion (and osmosis) As concentration gradient increases, the rate of diffusion increases. This is because there will be a greater net movement of particles from an area of high concentration to low concentration.

Factors that affect diffusion (and osmosis) As surface area to volume area decreases (i. e. the larger the organism), the rate of diffusion decreases. This is because it is faster for particles to reach the central parts (of the organism) from the surface area because the distance is short due to the small volume.

Diffusion and osmosis – summary (4 min) https: //www. youtube. com/watch? v=PRi 6 u. HDKe. W 4

Active transport Movement of particles against the concentration gradient (from a region of low concentration to a region of high concentration). This is an active process; it requires energy from respiration, and protein “pumps” located in the cell membrane.

Active transport– summary (3 min) https: //www. youtube. com/watch? v=e. De. Cg. TRFCb A

Movement across cells Task:

Movement across cells

Thumbs up or down Learning objectives: • Understand the three methods of movement of substances into and out of cells • Understand the importance of osmosis in plants • Understand the factors that affect the rate of movement of substances into and out of cells.