unit 2 - movement of substances

purpose of movement of substances across plasma membrane

1. to obtain nutrients → for energy and raw materials

2. to excrete waste products

3. to generate ionic gradients → essential for nervous and muscular activities

4. to maintain suitable pH and ionic concentration within cell for enzyme activity

what are the 2 types of processes that substances can be transported across plasma membrane

1. passive transport → movement of substances without expenditure of energy (diffusion and osmosis)

2. active transport → movement of substances involving expenditure of energy

what is diffusion

diffusion is the net movement of particles (atoms, ions, molecules) → from a region where they are of higher concentration → to a region where they are of lower concentration → that is down a concentration gradient → until equilibrium is reached

when does diffusion stop

down a concentration gradient → until all particles are evenly distributed → dynamic equilibrium (no net movement) → is reached

• dynamic equilibrium reached → particles are still in continual movement

what is concentration gradient

difference in concentration between two regions

• each type of particles moves down its own concentration gradient → independent of other concentration gradients

where does diffusion take place in

gas → fastest diffusion

liquid

solid → slowest diffusion

what are the 5 factors affected the rate of diffusion

1. molecular size

2. concentration gradient for molecule

3. kinetic energy of particles

4. diffusion distance

5. surface area-to-volume ratio

how does molecular size affect rate of diffusion

• different shapes → chains folded differently → different molecular size

smaller particle → higher rate of diffusion

• O2 (smaller) diffuse faster than CO2 (larger)

how does concentration gradient for molecule affect diffusion

greater/steeper the concentration gradient → higher rate of diffusion

how does kinetic energy of particles affect diffusion

higher temperature → particles have more energy and move faster → higher rate of diffusion

• very high temperature → can disrupt structure of membrane → lose its selectivity (allow all particles to go through)

how does diffusion distance affect diffusion

shorter diffusion distance → less time required for substance to travel → higher rate of diffusion

• diffusion → only effective over very short distances

how does surface area-to-volume ratio affect diffusion

larger surface area-to-volume ration → higher rate of diffusion

• object increase in size → surface area relative to volume/surface area-to-volume ration → gets smaller (it is a ratio!!!!!!!)

• some cells → specifically adapted → for absorption of substances → long narrow protrusions → increase surface area-to-volume ratio (root hair cell, epithelial cells of small intestine → microvilli)

what is the biological importance of diffusion in animals

• movement of oxygen in lungs to bloodstream and movement of carbon dioxide from bloodstream to lungs in human

• movement or absorption of soluble products of digestion → glucose and amino acids into villi and microvilli of small intestine

what is the biological importance of diffusion in plants

• gaseous exchange in leaves

  • in daylight → stomata open → allow carbon dioxide to diffuse into leaf → for photosynthesis → oxygen and water vapour → more concentrated in air spaces → diffuse out to drier air → outside stomata

  • diffusion → take place across cell membranes → gaseous exchange of oxygen and carbon dioxide at root hair cells

• movement of mineral salts from soil solution into root hair cells of plants

what is osmosis

osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane

what is a partially/selected permeable membrane

allows particles which are smaller than pores of membrane to pass through

• passage of large particles prevented (starch, sucrose, proteins)

• e.g plasma membrane, visking tubing, cellophane bag → particles e.g. glucose, iodine, salt, dissolved gases)

what is concentrations of solutions

• solute → dissolved in solvent → solution formed

• concentration of solution → amount of solute dissolved in a given volume of solvent

what is the water potential of a solution

measure of tendency of water molecules to move from one place to another

• of solution → cell sap of plant cell, cytoplasm of animal cell, soil solution

• H2O molecules → move from solution of higher water potential → to another of lower water potential → down water potential gradient → across partially permeable membrane

what is a dilute solution

what are the different types of solutions in terms of difference in concentrations

what are the factors affecting rate of osmosis

1. water potential gradient

2. distance over which water molecules need to move

3. surface area-to-volume ratio

how does water potential gradient affect osmosis

how does the distance over which water molecules need to move affect osmosis

how does surface area-to-volume ratio affect osmosis

what is the biological importance of osmosis to plants

how does some plants react to changes in turgor

how to answer osmosis questions

1. contrast of water potential → concentration is higher where and lower where?

2. movement of water molecules → where would the water molecules move from to where… via osmosis

3. what happens to the cell

what is active transport

how does active transport work

what is the energy needed for active transport

what are the proteins involved in active transport

what is the biological importance of active transport

what happens when a plant cell is placed in a dilute solution

what happens when a plant cell is placed in a concentrated solution

what happens when an animal cell is placed in a dilute solution

what happens when an animal cell is placed in a concentrated solution