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 What are the 3 main processes by which substances move within living organisms?

Diffusion, Osmosis and Active transport


What is active transport?

Active transpiort is the process whereby substances are absorbed against a concentration gradient eg. from an area of lower concentration to an area of higher concentration.


What is diffusion?

Diffusion is where particles move from an area of high concentration to an area where there's lower concentration.


   What is osmosis?

Osmosis is a special type of diffusion, which consists of the passive movement of water moleules across a partially permeable membrane, from a region of high water concentration to a region of low water concentration.


What is a partially permeable membrane?

A membrane with very small holes in it, so only tiny molecules (eg. water)  can pass through, and bigger molecules (eg. sucrose) can't.


Water molecules pass both ways through partially permeable membranes in osmosis.

True or false? And why?

true because water molecules move about randomly.


Fill in the gaps:

Because there will be more water ............ on one side of the membrane than on the other, in ........... there will be a steady ....... ........ of water into the region with ......... water molecules.

Because there will be more water molecules on one side of the membrane than on the other, in osmosis there will be a steady net flow of water into the region with fewer water molecules.


If there is a strong concentration of a sugar solution on one side of a membrane, and lots of water on the other side, how will osmosis impact on concentration?

The strong sugar solution will become more dilute, the water acts as though it is trying to make the concentration either side of the membrane more even.


How is the concentration of substances within cells regulated by osmosis?

Tissue fluid (water with oxygen, glucose and other substances dissolved in it) surrounds all the cells in the body. The tissue fluid will have a different concentration to the fluid inside cells, meaning if a cell is short of water and the solution is concentrated, the tissue fluid will be more dilute and will move into the cell by osmosis. If a cell has lots of water, the solution inside it will be dilute and water will be drawn out of the cell and into the fluid outside by osmosis.


Outline an experiment that can be conducted to show osmosis at work, using potatoes.

  1. Cut up a potato into identical cylinders, and get a number of beakers with different sugar solutions in them (with one being just pure water).
  2. Measure the length of the potato cylinders and leave a  few in each beaker for half an hour or so. Then take them out and measure their lengths again.
  3. If the cylinders have drawn water in by osmosis, they'll be longer than the original length, if the water has been drawn out they'll have shrunk.


How are exchange surfaces adapted to maximise effectiveness?

  1. They are thin, so substances only have a short distance to difffuse
  2. They have a larger surface so lots of a substance can diffuse at once
  3. Exchange surfaces in animals have lots of blood vessels, to get stuff in and out of the blood quickly.
  4. Gas exchange surfaces iin animals are often ventilated too - air moves in and out.


Which substances diffuse out of the underside of leaves?

Oxygen and Water vapour


How are leaves adapted to make them a good exchange surface?

  1. The underneath is covered in small holes called stomata, which are controlled by guard cells
  2. The flattened shape of the leaf increases surface area
  3. The walls of the cells inside the lead form another exchange surface, the air spaces inside increase the are of this surface so there's more chance for carbon dioxide to get into the cells.


How does water vapour leave plant leaves?

It evaporates from the cells inside the leaf, then escapes by diffusion because there's lots of water vapour inside the leaf and less of it in the air outside.


How are cacti adapted so that they don't lose water when they absorb gas and photosynthesise more effectively?

The cells on the stem of a cactus have stomata-like holes to let gases in. These holes only open at night, when it's cooler to prevent water being lost. Cacti are adapted so that they can store the CO2 that diffuses in at night until daylight when it's used for photosynthesis.


Where are the lungs situated in your body?

In the thorax (the upper part), separated from the abdomen by the diaphragm.


What happens to air in your body when you breathe it in?

The air travels down the trachea (windpipe), which splits into two tubes called 'bronchi', one going to each lung. The bronchi split into progressively smaller tubes called bronchioles, which end at small bags in the lungs called alveoli, where gas exchange takes place.


Draw and label a diagram of a cross section of the thorax (12 labels in total)


Outline the process of ventilation (both breathing in and breathing out)

Breathing in:

1) Intercostal muscles and diaphragm contract

2) Thorax volume increases

3) This decreases the pressure, drawing air in

Breathing out:
1) Intercostal muscles and diaphragm relax

2) Thorax volume decreases

3) This increases the pressure, so air is forced out


Which two pieces of technology can be used to assist people to breathe?

  • An 'iron lung' (no longer used)
  • A modern medical ventilator


Describe how an 'iron lung'/negative pressure ventilator used to work

They encased a person from the neck to their abdomen, with only the patient's head poking out. Air would be pumped out of the case, causing pressure to drop, the lungs of the patient to expand and air to be drawn into them. When air was pumped into the case, air would be forced out of the lungs as the pressure in the iron lung increased.


How do modern-day respirators/positive pressure ventilators work?

Most ventilators work by pumping air directly into the lungs. This expands the ribcage - when they stop pumping, the ribcage relaxes and pushes air back out of the lungs.


What are the advantages of using a modern-day medical ventilator rather than an iron lung?

  • They're portable
  • Don't confine the patients 
  • Useful during operations, when surgeons need access to the body


What are the risks of both forms of artificial ventilator?

Iron lung/negative pressure: Can interfere with blood flow in the abdomen, leading to the pooling of blood

Modern respirator/psitive pressure: Can occasinally cause damage (eg. burst alveoli) if the lungs can't cope with the artificial air flow


Draw and label a diagram of an alveoli, include the path of oxygen and carbon dioxide diffusion


How are alveoli specialised to maximise the diffusion of oxygen and carbon dioxide?

  • An enormous surface area (about 75m2 in humans)
  • A moist lining for dissolving gases
  • Very thin walls
  • A good blood supply


What are villi and how do they aid digestion?

Villi are tiny projections that cover the inside of the small intestine. They increase the surface are s digested food can be absorbed quicker into the blood. 

They have a single layer of surface cells and a very good blood supply to assist quick absorption.


Draw and label a cross section of a villus


Which plant cells are specialised for absorbing water and minerals?

Root hair cells


Why must root hairs absorb minerals using active transport? And why is this a slight disadvantage?

The concentration of minerals is usually higher in the root hair cell than in the soil arund it. Normal diffusion doesn't work because the minerals must be carried against the concentration gradient.


Active transport requires energy from respiration to work