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Analyse Transport Systems in Multicellular and Single-Celled Organisms

In this worksheet, students will analyse the impact of surface area to volume ratios on diffusion in organisms and the need for transport systems.

'Analyse Transport Systems in Multicellular and Single-Celled Organisms' worksheet

Key stage:  KS 4

GCSE Subjects:   Component 1: Concepts in Biology: Single Subject, Component 1: Concepts in Biology: Combined Science

GCSE Boards:   Eduqas

Curriculum topic:   Transport Systems

Curriculum subtopic:   Transport in Cells

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

All organisms need to transport substances around their cells to stay alive.  

Single-celled organisms use simple diffusion to move substances across their body surface, but when there are many cells, the volume increases meaning that the organism has a higher demand for supplies.

However, the surface area available for things to move through doesn’t increase with it, slowing down diffusion and potentially causing cell death.

 

To combat this, multicellular organisms increase their surface area to volume ratio by using specialised exchange surfaces and transport mediums to take substances in, out and around organisms, mostly by diffusion

 

Gas exchange in the alveoli

 

 

Gas Exchange

In mammalian gas exchange, specially designed alveoli increase the surface area of lung tissue connected to the capillary walls, aiding the uptake of oxygen by red blood cells and the removal of carbon dioxide from the pulmonary capillary blood.

 

In plants, however, carbon dioxide comes in and diffuses through the tissue fluid to the cells to be used for photosynthesis, while the oxygen made diffuses out to the surrounding tissues and into the environment using the concentration gradient.

 

 

Urea

Diffusion also helps to remove waste products like urea from protein breakdown -  blood transports it from the liver to the kidneys, where urea can be made into urine and excreted out of the body.

 

Intestinal villi

 

 

 Dissolved Food

When we eat, food is broken down in the digestive system into dissolved food molecules that diffuse from the gut lumen, across the wall of the small intestine and into the bloodstream.

The small intestine is the site of most food absorption and has specially designed microvilli that increase its surface area to maximise the amount of surface that interacts with the blood in absorption.

 

                          

Water transport via osmosis

The water content of a cell is determined by the water concentration surrounding it due to osmosis - the diffusion of water which relies strongly on concentration gradients.

 

osmosis in plant cells

 

Plant cells have strong permeable cell walls around the cell membrane that support the cell to prevent it from bursting during water uptake. This happens when plant cells are placed in dilute solutions which have a high water concentration. Osmosis occurs from the high volume of water on the outside into the lower concentration of water inside, causing the cell to fill up and become turgid.

 

But if plant cells are placed in solutions that are highly concentrated, meaning lots of solute but little water, cells release water by osmosis. This makes the cell vacuole and cytoplasm volume decrease and shrink away from the cell wall, making the cell flaccid, becoming plasmolysed. 

 

Osmosis

 

Animal cells don’t have cell walls, so osmosis can make the cell drastically change shape as it gains or loses water. This can affect their performance, for example red blood cells. Blood plasma and tissue fluid must be tightly controlled or else the red blood cell might gain too much water so that it could burst, or too much water is lost so that it shrivels up and stops being able to transport oxygen.

 

Root hair cells

 

Active transport of mineral ions

Sometimes diffusion isn’t enough, and energy has to be spent. In plants, the uptake of mineral ions by root hair cells is also dependent on active transport. Their large surface area makes them ideal for pulling mineral salts from a low concentration in the soil into the already highly saturated cells against the concentration gradient, using energy from respiration.  

 

There's a lot of information to take on board in this topic so it might be a good plan to read through this Introduction once more before having a go at the questions.

As soon as we have more than a few cells, specially designed transport systems are needed. 

How are different substances transported in and out of cells and the blood?

Which of these shows the journey of urea?

Blood ⇒ liver ⇒ kidneys

Liver ⇒ blood ⇒ kidneys

Kidneys ⇒ blood ⇒ liver

Active transport is a method of substance transport across exchange surfaces, for example between root hair cells and the soil.

Blood ⇒ liver ⇒ kidneys

Liver ⇒ blood ⇒ kidneys

Kidneys ⇒ blood ⇒ liver

What structures allow the intestines and lungs to increase their surface areas? 

Column A

Column B

The lungs have ...
alveoli
The small intestine has ...
microvilli

Both plants and mammals have very sophisticated methods of gas exchange because of the importance of effective respiration for cell survival.

Column A

Column B

In plant cells ...
carbon dioxide diffuses in and oxygen diffuses out...
In mammalian lungs ...
oxygen diffuses in and carbon dioxide diffuses out...

When placed in different solutions, cells change their shape due to the effect of osmosis.

In which of the conditions below, would it be most likely for a plant cell to become plasmolysed?

Drought or flood

Why is it that animal cells can burst if they take in too much water?

Drought or flood

Is it true or false that the cell wall controls substance diffusion? 

Drought or flood
  • Question 1

As soon as we have more than a few cells, specially designed transport systems are needed. 

CORRECT ANSWER
EDDIE SAYS
Single-celled organisms can easily exchange substances across their surface because the thickness of one cell is a short distance, so diffusion is fast. In more complicated creatures like humans, many layers of cells means that more time is needed for substances to travel to all the cells around the body, and more cells means a higher demand for nutrients. These two things together demonstrate the need for special transport systems to speed up the delivery of substances throughout organisms.
  • Question 2

How are different substances transported in and out of cells and the blood?

CORRECT ANSWER
EDDIE SAYS
How did you get on with this question? This is a summary of the different transport methods used by the key nutrients that cells need for them to be able to function. Diffusion is used in gas exchange with oxygen and carbon dioxide in both plants and animals, but also with dissolved foods across the small intestine wall, and waste products like urea. Osmosis is simply the diffusion of water and is important in determining cell shape. And finally, active transport is necessary for mineral ions to be transported into root hair cells in plants. This is because the concentration of mineral ions is higher in the plant cells than in the soil and so movement is against the concentration gradient.
  • Question 3

Which of these shows the journey of urea?

CORRECT ANSWER
Liver ⇒ blood ⇒ kidneys
EDDIE SAYS
This was quite a tricky question. How did you get on with it? When protein is broken down, any unused excess is converted into fat and carbohydrate stores, but this makes an unwanted byproduct called ammonia, which has to be made into urea so it can be safely removed. Urea is therefore made by the liver and then diffuses into the blood to be transported to the kidneys to be excreted out of the body.
  • Question 4

Active transport is a method of substance transport across exchange surfaces, for example between root hair cells and the soil.

CORRECT ANSWER
EDDIE SAYS
Active transport is a type of diffusion, but it's trying to fight natural concentration gradients in living organisms. When substances need to move substances into an already saturated area, simple diffusion won't work, so cells respire and use the energy gained to push substances against the concentration gradient from an area with low concentration to an area with a high one.
  • Question 5

What structures allow the intestines and lungs to increase their surface areas? 

CORRECT ANSWER

Column A

Column B

The lungs have ...
alveoli
The small intestine has ...
microvilli
EDDIE SAYS
The alveoli look like cotton plants or grapes, having a bumpy formation rather than being smooth spheres. This increases the amount of surface that has contact with the blood for optimum levels of diffusion. Microvilli also increase surface area. In the small intestine, this is to enable dissolved food molecules to diffuse into the blood. They create peaks and troughs in the lumen of the small intestine instead of a regular circular tunnel.
  • Question 6

Both plants and mammals have very sophisticated methods of gas exchange because of the importance of effective respiration for cell survival.

CORRECT ANSWER

Column A

Column B

In plant cells ...
carbon dioxide diffuses in and ox...
In mammalian lungs ...
oxygen diffuses in and carbon dio...
EDDIE SAYS
Plant cells take in carbon dioxide for photosynthesis, creating oxygen which diffuses out of the cells. But in the alveoli, in mammals, oxygen is needed for respiration while carbon dioxide waste is gathered in the blood from cells, carried to the lungs and breathed out.
  • Question 7

When placed in different solutions, cells change their shape due to the effect of osmosis.

CORRECT ANSWER
EDDIE SAYS
All these different phrases actually only refer to two different solutions, but it's important that your understanding of osmosis, concentration gradients and plant shapes is strong. Turgid means that the plant cell is full of water and the cell wall stops it bursting, as it would in a human cell. This happens when there is a lot of water around the cell, as in a low solute or a dilute solution. In these conditions, the cell takes up water across the concentration gradient through the permeable cell wall and partially permeable cell membrane. Plasmolysed is when the cell vacuole and cytoplasm have lost so much water that the cell membrane starts peeling off the cell wall as the cell shrinks. A cell loses water when osmosis takes water from the cell across a concentration gradient into an area with little water. This will be into a highly concentrated solution, meaning that there is a high concentration of the solute.
  • Question 8

In which of the conditions below, would it be most likely for a plant cell to become plasmolysed?

CORRECT ANSWER
Drought or flood
EDDIE SAYS
Can you remember what plasmolysed means? It is the word that describes the shrinking away of the cell vacuole and cytoplasm from the cell wall due to the loss of water from the cell. It occurs if the cell loses too much water, so if the soil is very dry because there hasn't been any rainfall for a long time, the cell will lose water down the concentration gradient to the surrounding environment by osmosis. Well done on making it through this activity! Remember to jot down any useful phrases or explanations that have helped you to get your head around this topic!
  • Question 9

Why is it that animal cells can burst if they take in too much water?

CORRECT ANSWER
EDDIE SAYS
The additional support provided by the cell wall gives plant cells strength, so that when they take up water by osmosis they don't burst, which is a problem in humans, such as in the red blood cells.
  • Question 10

Is it true or false that the cell wall controls substance diffusion? 

CORRECT ANSWER
EDDIE SAYS
The cell wall is permeable, meaning that it lets everything through for the partially permeable cell membrane within to deal with. Remember: the role of the cell wall is to provide support for the cell!
---- OR ----

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