Human Interactions

Describe the process of gas exchange in the lungs.

Oxygen enters the lungs and diffuses into the alveoli. Carbon dioxide diffuses out of the alveoli.

Describe the movement of particles in liquids and gases.

Particles in a liquid can move past each other whereas particles in a gas can move freely. Particles in both move randomly in all directions.

Explain why a stain is added to a specimen on a microscope slide.

To allow the structures to be seen more easily.

Diffusion

the spreading out of particles, of liquid or gas, resulting in net movement from an area of high concentration to low concentration

Diffusion can occur through…

a selectively permeable membrane, such as a cell membrane

During gas exchange, oxygen and carbon dioxide…

diffuse between the alveoli and the blood

Urea (a waste product made by cells) diffuses from the cells into the blood so it can then…

travel to the kidneys and excreted from the body.

The rate of diffusion can be increased by:

An increase in temperature

An increase in the concentration gradient (the difference between the high and low concentration

An increase in surface area

Surface area to volume ratio can be calculated by…

dividing the surface area by the volume of a cell, an organ or organism

Ratio =

Surface area divided by

Volume

Explain how increasing the temperature increases the rate of diffusion

Particles gain more kinetic energy, so the particles move more and therefore spread out more quickly.

Describe and explain the effect of increasing the surface area of an object on the rate of diffusion.

Increasing the surface area increases the rate of diffusion

This is because there is more surface available for diffusion to take place across

Describe and explain the effect of increasing the concentration gradient on the rate of diffusion

Increasing the concentration increases the rate of diffusion

This is because there is a larger difference in concentration

Unicellular organisms have a relatively high surface area to volume ratio, which allows…

efficient diffusion of required

substances

Large multicellular organisms generally have a lower surface area to volume ratio but many have adaptations that…

increase their surface area to allow more efficient diffusion

Cell membranes are often very thin, creating a…

very short path for diffusion

Alveoli in the lungs maximise the…

surface area

Gills are also structured to have a…

large surface area

Alveoli and gills both have an efficient blood supply, which helps to…

maintain a large concentration gradient as substances are carried away quickly

State the function of alveoli and gills.

gas exchange

State and explain how the following structures have adapted to maximise efficient diffusion in larger multicellular organisms:

Cell membranes

Blood supply

Structures with projections/finger like shape

a) Thin membrane for short diffusion pathway

b) Good blood supply to maintain concentration gradient

c) These structures have a large surface area for maximum diffusion

State where oxygen diffuses to, from the alveoli, during inhalation.

Capillaries/the blood

Describe the shape of a villi in the small intestine. Explain why this shape helps diffusion to take place

Finger-like projection - increases surface area

Explain how the human respiratory system is adapted to maximise the rate of gas exchange (give three adaptations).

Large number of alveoli to increase surface area

Alveoli/capillaries have thin walls to reduce diffusion distance

Good blood supply to maintain concentration gradient

All of these adaptations increase the rate of diffusion, which means there is a greater rate of gas exchange

Explain how gills in fish are adapted to maximise the rate of gas exchange.

Gill filament shape provides a large surface area

Gill cell membranes have thin walls to reduce diffusion distance

Good blood supply to maintain concentration gradient

All of these adaptations increase the rate of diffusion, which means there is a greater rate of gas exchange

Explain how the small intestine is adapted for efficient absorption of nutrients into the blood by diffusion.

Villi folds provide a large surface area

Walls of villi are thin to reduce diffusion distance

Good blood supply to maintain concentration gradient

All of these adaptations increase the rate of diffusion

Name the organelles that are found in plant cells but not animal cells.

cell wall, chloroplast, vacuole

Describe the role of the vacuole in plant cells.

Vacuoles store food materials, toxic substances, and unwanted materials.

State the word equation for photosynthesis.

carbon dioxide + water → glucose + oxygen.

Explain why photosynthesis is important for food chains.

Plants and algae make food via sunlight energy and photosynthesis and this increases their biomass - which is an important source of food and energy for animals.

Osmosis

the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane

a partially permeable membrane

is a membrane that lets particular substances through it, either in or out

A hypertonic solution is one in which…

the external solution has a higher concentration of solute than the cell (e.g. salt water)

A hypotonic solution is one in which…

the external solution has a lower concentration of solute than the cell (e.g. distilled water)

An isotonic solution is one in which…

the external solution has the same concentration of solute as the cell

Osmosis causes different effects in plant and animal cells because of the organelles they contain. This is because…

plant cells contain a cell wall which provides strength and support and a permanent vacuole which can store cell sap

cells losing water become…

flaccid

cells gaining water become…

turgent

hypertonic blood cells -

shrivelled

isotonic blood cells -

normal

hypotonic blood cells -

lysed (burst)

Explain how an increase in water concentration in the blood affects the size of a red blood cell.

The blood has a higher concentration of water

This means that water moves from the blood into the red blood cell via osmosis

The red blood cell swells (gets bigger)

Explain the movement of water from the soil into a root hair cell after a rainy day.

The soil has a higher concentration of water than the root hair cell

This means that water moves into the root hair cell via osmosis

Explain what will happen if a plant cell is placed into an isotonic solution.

The concentrations of solute inside and outside of the cell are equal

This means there will be no net movement of water

Calculating percentage change in mass

% Increase = Increase / x 100

Initial number

We will be investigating the effect of changing concentrations of salt solutions on the mass of potato tissue. State the:

Independent variable

Dependent variable

Two control variables

The concentration of salt solution

Change in mass of the potato

Any two of the following: Temperature, volume of the salt solution, initial mass of the potato cylinder

What would happen to the mass of a piece of potato if it was put into a hypotonic solution?

Water from the solution would move via osmosis into the potato so the potato would gain mass

What would happen to the mass of a piece of potato if it was put into a hypertonic solution?

In a hypertonic solution water would move out of the potato via osmosis so the potato would lose mass.

Name the piece of equipment used to cut cylinders from potato.

Cork borer

A student investigated the effect of different concentrations of sugar solution on pieces of potato. When the student lifted the potato out of the solution, explain why the student dried each piece of potato before weighing it.

To remove excess water on the outside of the potato because otherwise this would increase the mass

In the potato investigation, percentage change is calculated.

Explain why percentage change is calculated.

plant samples may not have exactly the same mass; using percentage change means we can compare results between different groups.

this means our results are more reproducible

Describe the change which will occur if a piece of peeled potato is placed in a concentrated sugar solution and explain why this change occurs.

The piece of potato will shrink

Because the concentration of sugar is greater in the solution than concentration inside the cell (or the concentration of water is higher inside the cell than in the solution)

So, water moves out of the cell via osmosis

Describe where cells get energy.

glucose and other food molecules

Active transport

is the movement of substances from a more dilute solution to a more concentrated solution, requiring energy from respiration

Active transport works against the…

concentration gradient

Active transport is used in root hair cells to… Concentration of mineral ions in the soil is… than inside the cell

absorb mineral ions from the soil… lower

Active transport is used in the villi in the

small intestine to…

transport glucose from the inside of the small intestine into blood vessels.

Active transport occurs when…

molecules move in the opposite direction of the concentration gradient

Active transport is required in the small intestine when…

the concentration of glucose is higher in the bloodstream than the small intestine

What best explains the difference between diffusion and active transport?

Active transport requires energy from respiration but diffusion does not

Explain why root hair cells contain many mitochondria.

Active transport requires energy as molecules are moving against the concentration gradient

Energy comes from respiration, so many mitochondria are needed

Explain why the concentration of oxygen in the cells in the small intestine can affect the rate of active transport of glucose into the blood.

Active transport requires energy as molecules are moving against the concentration gradient

Energy comes from respiration which requires oxygen, so the greater the oxygen concentration present, the greater the rate of respiration

Diffusion does not require energy because…

It is more important that the cell keeps the energy to use in respiration.