Diffusion-Specialised Structures

• What process do plants use to produce their own food?

  Photosynthesis
• What gas is required by plants for photosynthesis as a reactant?

  Carbon dioxide
• How does carbon dioxide enter the leaves of plants?

  By diffusing through the stomata
• What are stomata?

  Tiny openings or pores
• Where are stomata usually found on the leaf?

  On the underside of the leaf surface
• What waste product of photosynthesis diffuses out of the stomata?

  Oxygen
• Why do many plants have broad, flat leaves?

  To increase surface area for carbon dioxide diffusion
• Where does carbon dioxide diffuse through?

  The stomata
• What is the function of the spongy mesophyll layer in the leaf?

  It contains air spaces for gas movement
• What do air spaces in the spongy mesophyll layer allow gases to do?

  Move around more smoothly
• What do the air spaces in the spongy mesophyll help to maintain?

  A steep concentration gradient
• What process is the small intestine responsible for?

  Absorbing digested food molecules
• How long can the small intestine be in humans?

  Up to 5m long
• What ensures that diffusion of food molecules occurs quickly and efficiently?

  Adaptations of the small intestine
• What increases the surface area of the small intestine?

  Many finger-like villi structures
• What do villi provide more space for?

  Molecules to pass through the membrane
• What is increased by the many features of the villi?

  Rate of diffusion
• How thick are the walls of the villi?

  One cell thick
• What does the thinness of the villi walls ensure?

  A short diffusion pathway
• What surrounds the villi?

  Many blood capillaries
• What is transported away by the blood capillaries?

  Absorbed food molecules
• What do the blood capillaries help maintain by transporting absorbed food molecules away?

  A steep concentration gradient
• What are the cells that make up the lining of the villi covered in?

  Microvilli
• What do microvilli increase?

  The surface area of the cell membrane
• Where are the lungs located?

  In the chest
• What happens when you inhale?

  Air is taken into the lungs
• What diffuses into the bloodstream from the air in the lungs?

  Oxygen
• What do oxygen molecules bind to in the red blood cells?

  Haemoglobin
• What is transported around the body by the red blood cells?

  Oxygen
• What waste product of respiration diffuses from the bloodstream into the lungs?

  Carbon dioxide
• How is carbon dioxide removed from the body?

  When you breathe out
• What is the exchange of oxygen and carbon dioxide in the lungs known as?

  Gas exchange
• What are the lungs adapted to carry out?

  Gas exchange
• What tiny air sacs do the lungs contain?

  Alveoli
• What is the surface of each alveolus like?

  Very small with a folded surface
• What do millions of alveoli give each lung?

  A very large surface area
• What surrounds the alveoli?

  A network of blood capillaries
• What is maintained by the continuous movement through the blood vessels?

  A steep concentration gradient
• Where is a steep concentration gradient maintained?

  Between the alveoli and bloodstream
• How thick are the membranes of the alveoli and the capillaries?

  Just one cell thick