4.1.3.1 Diffusion
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What is diffusion?
• gradual movement of particles from an area of higher concentrations to an area of lower concentrations
Where does diffusion happen and why?
• in solutions and gases • particles in the substances are free to move
What is the simplest type of diffusion?
• different gases diffuse through each other
What is a concentration gradient?
• the difference in concentration
What does a bigger concentration mean for the rate of diffusion?
• the diffusion rate is faster
What a higher temperature mean for the rate of diffusion?
• the diffusion rate is faster because the particles have more energy
What do cell membranes do?
• they hold the cell together • they let dissolved substances move in and out of the cell by diffusion
What small molecules can diffuse through cell membranes?
• oxygen • glucose • amino acids • water
What does it mean if there a lot more particles on one side?
• there is a net (overall) movement from that side
What does a large surface area mean for the rate of diffusion?
• the diffusion rate is faster because more particles can pass through at once
What is exchange surfaces?
• how easily something moves between an organism and its environment depending on its surface area to volume ratio
Why can enough substances be exchanged across a membrane in a single-celled organism?
• it has a large surface area compared to volume
Why can’t enough substances be exchanged across a membrane in multicellular organisms?
• they have a smaller surface area compared to volume
What does a multicellular organism do for efficient diffusion?
• exchange surface
How are exchange surfaces adapted to maximise effectiveness?
• thin membrane so substances have a short distance to diffuse • large surface area so lots of substances can diffuse at once • exchange surfaces in animals have lots of blood cells to get things into and out of the blood quickly • gas exchange surfaces in animals (alveoli) are often ventilated
What are alveoli specialised for?
• to maximise the diffusion of oxygen and carbon dioxide
How are alveoli adapted to do their function?
• an enormous surface area (around 75 meters squared) -moist lining for dissolving gases • very thin walls • good blood supply
What is a villi’s function?
• to absorb digested food quicker into the blood
How are villi adapted to do their funtion?
• single layer of surface cells • good blood supply to assist quick absorption • large surface area
What are the exchange surfaces of a leaf?
• the underneath of the leaf as it is covered in stomata which carbon dioxide diffuses through • walls of the cells inside as the air spaces inside increase the area of the surface so there is more chance for carbon dioxide to get into the cell
What are the gills’ function in a fish?
• gas exchange surface • water enters the fish through mouth and passes through the gills, oxygen diffuses into the blood and carbon dioxide diffuses into the water
What are the adaptations of gills?
• gills made up of gill filaments which increase surface area for exchange of gases • gill filaments covered in lamellae which increases surface area even more lamellae have lots of blood capillaries to speed up diffusion • lamellae have a thing surface layer of cells to minimise distance • blood flows through lamellae in one direction and water in the other for a large concentration gradient • concentration of oxygen in water is higher than blood so as much oxygen diffuses into blood