Topic 1b-Transport in Cells Flashcards Preview

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What is diffusion?

The movement of substances into and out of cells across the cell membranes.


What is the definition of diffusion?

DIFFUSION is the SPREADING OUT of PARTICLES of any substance in solution, or particles of gas, resulting in a net movement from an area of HIGHER CONCENTRATION to an area of LOWER CONCENTRATION.


What does diffusion occur in?

Diffusion happens in both SOLUTIONS and GASES-that's because the particles in these substances are free to MOVE ABOUT randomly.


What is the simplest type of diffusion?

The simplest type is when different GASES diffuse through each other.


What factors affect the rate of diffusion?

1) The difference in concentrations (CONCENTRATION GRADIENT). The bigger the concentration gradient, the faster the diffusion rate. This is because the net movement from one side is greater.

2) The TEMPERATURE. A higher temperature will also give a faster diffusion rate because the particles have more kinetic energy, so move around faster.

3) The SURFACE AREA of the membrane. The larger the surface area (e.g. of the cell membrane), the faster the rate of diffusion. This is because more particles can pass through at once.


What substances in the human body are transported by diffusion?

Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney. (on spec!!)


How does a cell membrane help in the process of diffusion?

1)They let stuff move both IN and OUT of the cell.

2) Dissolved substances can move in and out of the cells by DIFFUSION.

3) Only very SMALL molecules can DIFFUSE through cell membranes-things like OXYGEN (needed for respiration), GLUCOSE, AMINO ACIDS and WATER.

4) BIG molecules like STARCH and PROTEINS can't fit through the membrane.

5) Just like with diffusion in air, particles flow through the cell membrane from where there's a HIGHER CONCENTRATION to where there's a LOWER CONCENTRATION.

6) They're only moving about RANDOMLY of course (gas particles), so they go BOTH ways-but if there are a lot MORE particles on one side of the membrane, there's a NET (overall) movement FROM that side.

7) The LARGER the SURFACE AREA of the membrane, the FASTER the diffusion rate, because more particles can pass through at once.


How is a single-celled organism adapted for diffusion?

A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.


Why are exchange surfaces important?

-All living organisms rely on exchanges with the environment to survive.
However, diffusion only works efficiently if the distance over which the substances have to diffuse is small and the organism has a large surface area compared to its volume. This is the case for small organisms.


Why are multicellular organisms, surfaces and organ systems specialised for exchanging material?

For larger, more complex organisms – which have a small surface area:volume ratio and a bigger distance from the surface to the cells inside the body - diffusion alone is insufficient to meet the needs of all cells.

As larger organisms evolved, specialised organ systems - with surfaces across which substances could be exchanged efficiently - also evolved. These specialised organ systems were needed in order to transport substances around the organisms.


How are multicellular organisms, surfaces and organ systems specialised for exchanging material?

1) Having a LARGE SURFACE AREA for greater exchange (achieved by having a folded surface.)

2) Having a THIN exchange surface for a SHORT DIFFUSION distance. E.g. a membrane that is thin, to provide a short diffusion path

Animals also further maximise the efficiency of exchange by:

3) Exchange surfaces in ANIMALS have LOTS OF BLOOD VESSELS, to get stuff into an out of the blood quickly.

4) Maintaining VENTILATION of the surface (at gas exchange surfaces) through breathing - this always ensures that a concentration gradient is maintained.


Is energy needed for diffusion to occur?

It is 'easy' for molecules to move down the concentration gradient so this is a PASSIVE process, which means that it does not need any energy from respiration.


Define osmosis...

OSMOSIS is the MOVEMENT OF WATER MOLECULES across a PARTIALLY PERMEABLE MEMBRANE from a region of HIGHER WATER CONCENTRATION (a dilute solution) to a region of LOWER WATER CONCENTRATION (a concentrated solution).


What's a partially permeable membrane?

A PARTIALLY PERMEABLE membrane (like the cell membrane) does not let all types of particles through.

It has small pores/gaps within it which control the movement of particles from one side to the other. It is sometimes called SELECTIVELY PERMEABLE MEMBRANE since it selects which particles can pass through.

The pores are so small, that only tiny MOLECULES (like water) can pass through them, and bigger molecules (e.g. sucrose) can't.


In which direction do the water molecules pass through the membrane?

The water molecules actually pass BOTH WAYS through the membrane during osmosis. This happens because water molecules MOVE ABOUT RANDOMLY all the time.


Does osmosis require energy?

Osmosis is a type of diffusion, so it is a PASSIVE PROCESS (it does not need energy to occur).


What happens if a cell is put in a solution with a higher water concentration than itself?

If a cell is put in a solution with a higher water concentration than itself, water moves into the cell and it bursts.


What happens if a cell is put into a solution with the same water concentration as itself?

if a cell is put into a solution with the same water concentration as itself, water moves in and out at an equal rate so the cell remains the same.


What happens if a cell is put into a solution with a lower water concentration than itself?

If a cell is put into a solution with a lower water concentration than itself, water moves out of the cell and it shrivels up.


Practical-Observing the effect of sugar solutions on plant tissue

What is the method?

1) Osmosis ONLY involves water molecules-nothing else. Osmosis is water diffusion.

2) Osmosis occurs across a barrier such as a cell membrane which is 'selectively permeable', which means it only lets through small water molecules.

1) First cut up a POTATO into IDENTICAL CYLINDERS.
And get some beakers with DIFFERENT SUGAR SOLUTIONS in them. One should be PURE WATER and another should be a VERY CONCENTRATED SUGAR SOLUTION (e.g. 1 mol/dm3). Then you can have a few others with concentrations IN BETWEEN (e.g. 0.2 mol/dm3, 0.4 mol/dm3, 0.6 mol/dm3, etc).

2) You measure the MASS of the cylinders, then leave one cylinder in each beaker for 24 hours or so .

3) Then you take them out, DRY them with a paper towel and measure their masses AGAIN.


What does the final mass indicate?

How can you calculate the percentage change?

-If the cylinders have drawn in water by osmosis, they'll have INCREASED IN MASS. If water has been drawn out, they'll have DECREASED IN MASS.

You can calculate the PERCENTAGE CHANGE IN MASS, then plot a GRAPH.

- Percentage change=

final value - original value
______________________ x 100
original value


What do the results conclude?

The water molecules enter through the partially permeable membrane down their CONCENTRATION GRADIENT. The potato will swell up with the extra water, and so get bigger-and heavier. It's also really firm, because all its vacuoles are swollen with water. This is called TURGID.

Eventually there will be no difference between the concentrations outside and inside.

The opposite will happen if the potato is put into a concentrated solution, like really syrupy sugar solution-the potato cells lose their water- so the potato is FLACCID.


What are the dependent and independent variable of this experiment?


The INDEPENDENT VARIABLE is the CONCENTRATION of the sugar solution. All OTHER variables must be kept the SAME in each case or the experiment won't be a FAIR TEST.


What were the risks involved in this experiment?

Risk assessment:
If you're using a knife, make sure you cut away from yourself and that the blade is clean and sharp.


What errors could occur?

You need to be aware of how the errors may arise. Sometimes they may occur when CARRYING OUT THE METHOD, e.g. if some potato cylinders were not FULLY DRIED, the excess water would give a HIGHER MASS, or if water EVAPORATED from the beakers, the CONCENTRATIONS of the sugar solutions would change.


How can you reduce the effect of the errors?

You can REDUCE THE EFFECT of these errors by REPEATING the experiment and calculating a MEAN PERCENTAGE CHANGE at each concentration.


What happens to the the levels of glucose, water and ions when exercising for long periods?

During extended periods of exercise, an athletes body changes:
- the athlete uses up much of the GLUCOSE in their body during RESPIRATION.
-the athlete generates heat as they respire more
-the athlete sweats more to try to cool themselves down (this sweating results in loss of water and mineral IONS, e.g. sodium)


What do sports drinks contain and do?

-Sports drinks contain sugars to replace the glucose used in respiration to make energy.
-They also contain water and ions to replace those lost during sweating. The cells work less efficiently if these are not available.
-Sugars and ions can move into the cells by diffusion and water moves by osmosis.

1) Sugar keeps glucose levels high
2)water, sugar and ions passing into the blood stream and then cells
3)water helps absorb nutrients
4)sugar helps athlete continue exercising for longer
5) water moistens lungs for breathing
6) water helps regulate body temperature
7) Ions keep cells working properly especially those in nervous system


Define active transport...

Active transport is the MOVEMENT of particles AGAINST a CONCENTRATION GRADIENT (i.e. from an area of LOW concentration to an area of HIGHER concentration/ from a more dilute solution to a more concentrated solution.

This requires ENERGY transferred from RESPIRATION.


Describe the purpose of a root hair cell and how are plant roots adapted to maximise the exchange of substances?

Why can't root hair cells use diffusion to take up minerals from the soil and what is used instead?

-The cells on the surface of plant roots grow into long "HAIRS" which stick out into the soil. Each branch of a root will be covered in MILLIONS of these microscopic hairs.

This gives the plant a LARGE SURFACE AREA for absorbing WATER and MINERAL IONS from the soil.

-However, the concentration of minerals is usually HIGHER in the ROOT HAIR CELLS than in the SOIL around them, so the root hair cells CANNOT use DIFFUSION to take up minerals from the soil.

-Instead they use ACTIVE TRANSPORT.


Why do plants require ions?

Plants NEED mineral ions for HEALTHY GROWTH.


How do root hair cells absorb minerals ions using active transport?

Active transport allows the plant to absorb mineral ions from a very DILUTE solution, against a concentration gradient. This is essential for its growth.

But active transport needs ENERGY from RESPIRATION to make it work.


Does active transport occur in humans?

Active transport also happens in HUMANS.


Give an example of the use of active transport in humans...

In humans active transport is used when taking in GLUCOSE from the GUT. When theres a low conc of nutrients (e.g. glucose) in the gut compared to a high conc in blood stream.


When is active transport used in the digestive system?

ACTIVE TRANSPORT is used in the digestive system when there is a LOWER CONCENTRATION of nutrients in the gut, but a HIGHER CONCENTRATION of nutrients in the BLOOD.


How does active transport work in the digestive system?

1. When there's a HIGHER CONCENTRATION of glucose and amino acids in the gut they DIFFUSE NATURALLY into the blood.

2. But- sometimes there's a LOWER CONCENTRATION of nutrients in the gut than there is in the blood.

3. This means the CONCENTRATION GRADIENT is the wrong way. The nutrients should go the other way if they followed the rules of diffusion.

4. The same process used in plant roots is used here... ACTIVE TRANSPORT.

5. Active transport allows nutrients to be taken into the blood despite the fact that the CONCENTRATION GRADIENT is the wrong way.


Why is active transport so important in humans?

This is essential to stop us starving. It means that GLUCOE can be taken into the bloodstream when its concentration in the blood is already HIGHER than in the gut. The glucose can then be transported to cells, where it's used for RESPIRATION.


Tip- Active transport comes in useful for loads of processes in the body. E.g. it's used in the kidneys to reabsorb useful substances, like glucose and ions, when making ions.

Tip- water is taken into root hair cells by osmosis.


Describe how active transport takes place...

1. Active transport takes place through CELL MEMBRANES.

2. It needs special proteins celled CARRIER PROTEINS.

3. The particle to be transported is GRABBED by the carrier protein.

4. The carrier protein is given ENERGY from a special molecule called ATP.

5. The carrier protein ROTATES in the MEMBRANE and RELEASES the particle to the other side.

6.The carrier protein rotates back again and can transport another particle.


Summarise the transport methods...

1) Diffusion -Movement of PARTICLES from an area of HIGHER CONCENTRATION to an area of LOWER CONCENTRATION.
-DOESN'T require energy.

2) Osmosis- Movement of WATER MOLECULES across a PARTIALLY PERMEABLE MEMBRANE from a region of HIGHER water concentration to a region of LOWER water concentration.
-DOESN'T require energy.

3) Active transport -Movement of PARTICLES (ions or dissolved molecules) AGAINST a CONCENTRATION GRADIENT (so low to high).
-REQUIRES ENERGY (transferred during respiration).


What substances move in and out of cells by diffusion?

Tip- gas exchange in animals means taking in oxygen from the environment and releasing carbon dioxide.

-OXYGEN and CARBON DIOXIDE are transferred between CELLS and the ENVIRONMENT during GAS EXCHANGE.

-In humans, UREA (a waste product produced from the breakdown of proteins) diffuses from CELLS into the BLOOD PLASMA for removal from the body by the kidneys.


Why is surface area to volume ratio important when considering the time for substances to be transported?

How EASY it is for an organism to exchange substances with its environment depends on the organism's SURFACE AREA TO VOLUME RATIO.


How do you calculate the surface area to volume ratio?

-The volume of a block (e.g. a cube or cuboid) is found by the equation:

volume = length x width x height

-The area of a square or rectangular surface is found by the equation :

area = length x width

To calculate the surface area of an object, just calculate the area of each side and add them all together.


What is the job of the lungs?

The job of the lungs is to transfer OXYGEN to the BLOOD and to remove WASTE CARBON DIOXIDE from it.


What do the lungs contain to help in gas exchange?

To transfer O2 and remove CO2 the lungs contain millions of little air sacs called ALVEOLI where GAS EXCHANGE takes place.


Explain how alveoli assist in gas exchange?

The alveoli are surrounded by a network of tiny blood vessels known as capillaries. There is a higher concentration of oxygen in the air than in the blood, so oxygen diffuses out of the air in the alveoli and into the blood capillaries. Carbon dioxide diffuses in the opposite direction. Air enters and leaves the alveoli via small tubes called bronchioles.


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

They have:
1) An enormous surface area- each alveolus is folded, providing a much greater SURFACE AREA.

2) Very thin walls- the walls of the alveoli are THIN, shortening the diffusion distance across which gases have to move.

3) A good blood supply- each alveolus is surrounded by BLOOD CAPILLARIES which ensure a good blood supply. This is important as the blood is constantly taking oxygen away and bringing in more carbon dioxide-which helps to maintain the maximum concentration gradient between the blood and the air in the alveoli.

4) Ventilation- each alveolus is ventilated, removing waste carbon dioxide and replenishing oxygen levels in the alveolar air. This also helps to maintain the maximum concentration gradient between the blood and the air in the alveoli.

5) A MOIST LINING for dissolving gases.


What does the small intestine absorb?

How is the small intestine adapted to absorb stuff?

-Nutrients, e.g. GLUCOSE and AMINO ACIDS, are absorbed into the bloodstream from the SMALL INTESTINE- either by diffusion or active transport.

-To aid this absorption, the inside of the small intestine is covered in millions and millions of tiny little projections called VILLI.


What are villi?

Villi are folds within the wall of the small intestine across which digested food molecules are exchanged between the gut and the bloodstream.


What is the role of vili in the absorption of nutrients in the small intestine?

How are they adapted?

Tip-It's one villUS and two or more villi.

Villi increase the surface area in a big way so that digested food is ABSORBED much more quickly into the BLOOD.

Notice they have:
- a SINGLE layer of surface cells increases the surface area.
-the villi wall is THIN to provide a short diffusion path.


Describe how and why carbon dioxide and oxygen are exchanged between plants and the air?

Plants need CARBON DIOXIDE for photosynthesis. Carbon dioxide DIFFUSES INTO THE AIR SPACES within the leaf, then it DIFFUSES INTO THE CELLS where photosynthesis happens. The leaf's structure is adapted so that this can happen easily.


How are leaves adapted to maximise the exchange of gas in plants?

-The underneath of the leaf is an EXCHANGE SURFACE. It's covered in little holes called STOMATA which which the carbon dioxide diffuses in through.

OXYGEN (produced in photosynthesis) and WATER VAPOUR also diffuse OUT through the stomata. (Water vapour is actually lost from all over the leaf surface, but most of it is lost through the stomata.)

- The FLATTENED SHAPE of the leaf increases the AREA of this exchange surface so that it's more effective.

- The WALLS OF THE CELLS inside the leaf form another exchange surface. The AIR SPACES inside the leaf increase the AREA of this surface so there's more chance for carbon dioxide to get into cells.

- Leaves are THIN to provide a short diffusion path.


How does water vapour leave the leaf?

The water vapour EVAPORATES from the cells inside the leaf. Then it escapes by DIFFUSION because there's a lot of it INSIDE the leaf and less of it in the AIR OUTSIDE.


Where does water exit a plant?
How is water loss in plants controlled?

Water vapour is lost from all over the leaf surface, but most of it is lost through the stomata.

If the plant is losing water faster through its leaves than it can be replaced by the roots, the stomata can be closed by GUARD CELLS.

Without these guard cells, the plant would soon lose so much water that it would WILT (droop).


How do fish exchange gas?

What is the gas exchange surface?

Fish exchange oxygen and carbon dioxide between blood and water by DIFFUSION. There's a lower concentration of oxygen in WATER than in the air. So fish have special adaptations to get enough of it.

In a fish the gas exchange surface is the GILLS.


Where are the gills located?

The gills are located inside a fish's head. Water flows in through the mouth, over the gills and out through the openings behind the head.


What is the structure of gills?

Water (containing OXYGEN) enters the fish through its MOUTH and passes out through the GILLS. As this happens, OXYGEN diffuses from the water into the blood in the gills and CARBON DIOXIDE diffuses from the blood into the water.


How are gills adapted to exchange gases?

1) Each gill is made of lots of thin plates called GILL FILAMENTS, which give a BIG SURFACE AREA for EXCHANGE of GASES.

2) The gill filaments are covered in lots of tiny structures called LAMELLAE, which INCREASE the SURFACE AREA even more.


4) They also have a THIN MEMBRANE to provide a short diffusion path.

5) BLOOD flows through the lamellae in one direction and WATER flows over in the opposite direction. This maintains a LARGE CONCENTRATION GRADIENT between the water and the blood.

6) The CONCENTRATION OF OXYGEN in the WATER is always HIGHER than that in the BLOOD, so as much oxygen as possible diffuses from the water into the blood.


Where are the lungs located and what is the structure of lungs in mammals?

The lungs are located within the upper part of the body called the THORAX. They are surrounded by the RIBCAGE (which protects them) and in between the ribs are INTERCOSTAL MUSCLES which play a role in ventilating the lungs.

Beneath the lungs is a muscular sheet called the DIAPHRAGM. This separates the lungs from the abdomen of the body and also plays a role in ventilating the lungs.


What is ventilation?

Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs. Take care - this is called breathing or ventilation, not respiration


What happens when we inhale?

1) The intercostal muscles CONTRACT, expanding the RIBCAGE OUTWARDS and UPWARDS.

2) The diaphragm contracts and becomes flatter to INCREASE THE VOLUME of the chest.

3) PRESSURE INSIDE THE CHEST IS LOWERED and air is sucked into the lungs.


What happens when we exhale?

1) The intercostal muscles RELAX, the RIBCAGE DROPS INWARDS and DOWNWARDS.

2) The diaphragm relaxes, becoming dome shaped to DECREASE THE VOLUME of the chest.



What is the function of roots?

Roots absorb WATER and MINERAL IONS from the soil.


How are roots adapted for exchanging materials?

1) Roots have root hair cells which provide a LARGE SURFACE AREA for absorption.

2) Root hair cells have THIN MEMBRANES to provide a short diffusion path.