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Explain Transport Systems in Multicellular and Single-Celled Organisms

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

'Explain 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 have a large surface area compared to their volume, so they can move substances across the cell membrane. However, multicellular organisms have a smaller surface area compared to their volume because the volume of  the cells increases while the surface area stays the same. This means that substances have to supply more needs and travel farther, slowing transport down.

 

To increase their surface area to volume ratio, they've got special exchange surfaces and transport mediums to move substances around, usually using diffusion.

 

 

Gas Exchange

When mammals breathe, specially designed alveoli increase the surface area for diffusion in the lungs, helping to take in oxygen and remove carbon dioxide.

In plants, carbon dioxide enters the leaves through stomata by diffusion, for photosynthesis. This produces oxygen which is released back into the air by diffusion.

 

 

Urea

Diffusion also helps to remove waste like urea, where blood transports it from the liver to the kidneys to be excreted out of the body.

 

 

Dissolved Food

 

Intestinal villi

 


Food is broken down in the digestive system into dissolved food molecules. These diffuse into the bloodstream using microvilli, which help to increase the gut's surface area for absorption.


 

 

 Water transport via osmosis

 

Osmosis

 

 

Osmosis is particular to the diffusion of water.

When plant cells are placed in a high concentration of water, they take water in and become turgid and the only thing that stops them bursting is their strong cell walls.

But if plant cells are placed in a low concentration of water, cells release water and they shrink away from the cell wall, becoming flaccid or plasmolysed.

Animal cells change shape during osmosis as they don't have cell walls - for instance, red blood cells will expand or shrivel up.

 

 

Active transport of mineral ions

In plants, the uptake of mineral ions by root hair cells uses active transport to pull them from a low concentration in the soil, into the already highly saturated cells. This goes against the concentration gradient and therefore needs energy from respiration. 

 


There's a lot to remember in this topic, so have another read through this Introduction to make sure you've got it, before moving on to some questions.

 

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

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

Which of these different substances are transported in and out of cells and the blood using diffusion?

Dissolved foods

Water

Oxygen

Urea

Mineral ions

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

Dissolved foods

Water

Oxygen

Urea

Mineral ions

Which of these shows the journey of urea?

Blood ⇒ liver ⇒ kidneys

Liver ⇒ blood ⇒ kidneys

Kidneys ⇒ blood ⇒ liver

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

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

Column A

Column B

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

Is it true or false that the cell wall blocks substances from diffusing across.

Column A

Column B

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

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

Column A

Column B

A plant cell in a low concentration of water becom...
shrinks
A plant cell in a high concentration of water beco...
turgid
An animal cell in a low concentration of water ...
flaccid or plasmolysed

Diffusion, osmosis and active transport all move substances down or against what phenomenon?

  • 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

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 3

Which of these different substances are transported in and out of cells and the blood using diffusion?

CORRECT ANSWER
Dissolved foods
Oxygen
Urea
EDDIE SAYS
Don't despair if you ticked water and got it wrong! Read to the end of this explanation and you'll see why it wasn't correct. 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. Water, although technically still moved by diffusion, has its own special term for this transport called osmosis. It's very important to get used to using the proper scientific terms in these questions. Finally, mineral ions are not transported by diffusion without help! Active transport is necessary for mineral ions to be transported into root hair cells in plants, and for that, they require energy.
  • Question 4

Active transport is a method of substance transport across exchange surfaces, for example, 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 cells need to move substances into an already saturated area, simple diffusion won't work, so they use energy to push substances against the natural concentration gradient from an area with little, to an area with a lot.
  • Question 5

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 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

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 8

Is it true or false that the cell wall blocks substances from diffusing across.

CORRECT ANSWER
EDDIE SAYS
How did you get on with this final question? The cell wall is permeable, meaning that it lets everything through for the partially permeable cell membrane within to sort. Remember: the role of the cell wall is to provide support for the cell! Well done on making it through this activity! Remember to jot down any useful phrases or explanations that have helped you get your head around this topic!
  • Question 9

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

CORRECT ANSWER

Column A

Column B

A plant cell in a low concentrati...
flaccid or plasmolysed
A plant cell in a high concentrat...
turgid
An animal cell in a low concentra...
shrinks
EDDIE SAYS
There was a right mixture of terms here from the everyday word 'shrinks' to some highly technical words like plasmolysed! Turgid means that the plant cell is full of water and the cell wall is the only thing that stops it bursting, as human cells would. This happens when there is a lot of water around the cell, called a dilute solution. The cell takes up water from the dilute solution across the concentration gradient, through the permeable cell wall and cell membrane. Plasmolysed is when the cell has lost so much water that the cell membrane starts peeling off the cell wall. A cell loses water when osmosis takes water across a concentration gradient from a high water concentration into an area with less water. In animal cells, this causes shrinkage.
  • Question 10

Diffusion, osmosis and active transport all move substances down or against what phenomenon?

CORRECT ANSWER
Concentration gradient
A concentration gradient
The concentration gradient
EDDIE SAYS
How did you get on? If you found it hard to answer this one, why not go back to the Introduction and have another read through before doing the questions. The movement of substances is often dependent on whether the outside environment has more or less of the desired molecule than what's inside the cell, creating a natural shift in particles to create an equal balance on both sides. Active transport takes this one step farther and uses energy to go against this natural desire for equilibrium.
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