Food Chains and Food Web

Changes in the Population of Living Things

This science revision note aims to help your child:

– Understand the different scientific terminologies relating to food chains and food web.

– Understand food chains (What does the arrow,—>, mean?)

– Predict what happens to the population of organisms.

– proper scientific keywords to explain the concepts clearly.

 

But before you read on, you might want to download this entire revision notes in PDF format to print it out for your child, or to read it later.

This will be delivered to your email inbox.

Some of the MUST-KNOW about Food Chains and Food Web Topic:

1) Understand the definition of the following:

    • Producer: plants that can make their own food
    • Consumer: animals that feed on other organisms
    • Predator: animals which feed on another animal
    • Prey: animal which gets eaten by another animal

2) Comprehend the relationship between the different organisms

3) Understand how to analyse a food chain/ food web

 

Question

Study the food web below.

Identify the prey(s) in the food web. Explain your answer.

STEP 1

Recall the definition of prey.

 

STEP 2

Identify the organisms that fit the definition of prey. Substantiate your answers with evidence from the food web.

 

FINALLY, put your answer together

Question: Identify the prey(s) in the food web. Explain your answer.

Answer: Organism X and Y are prey. Preys are animals that are eaten by another animals. Organism X and Y are both eaten by W which is a predator. Hence, X and Y are prey.

 

Common mistakes

Wrong answers: Organism X, Y, S and Z are preys.

Teachers’ comments: Organism S and Z are food producers. Food producers are not prey. Do refer to the definition of prey and predator at the beginning of this revision note.

 

 

Let’s Try Another Example!

Question

The food chain below shows the food relationship between plant P, animal Q and animal R.

A disease outbreak killed many animals Q. The disease does not affect plant P and animal R. The line graph below shows the change in the population of plant P and animal R over time.

 

Which line (1 or 2) shows the population change of Animal R? Explain your answer.

 

STEP 1

Identify the relationship between Animals Q and R.

To do this, examine the food chain.

The arrows in the food chain show the direction that which energy is transferred. Since the arrow is pointing from Q to R, energy is transferred from Q to R. This means that Animal R feeds on Animal Q.

 

Note: These are different ways to describe the food relationship between Animals R and Q.

Animal R feeds on Animal Q.

Animal Q is eaten by Animal R.

Animal Q is the prey of Animal R.

Animal R is the predator of Animal Q.

You can use any one of the above to answer this question.

 

STEP 2

Explain how Animal R will be affected when Animal Q decreases.

Animal Q decreases —-> Animal R will have less food to feed on —> Population of animal R will decrease.

 

STEP 3

To do so, examine the line graph and identify what each line shows.

  • Line 1 shows an increase in population
  • Line 2 shows a decrease in population

Hence, Line 2 shows the population change in the population of Animal R.

 

FINALLY, put your answer together

Question: Which line (1 or 2) shows the population change of Animal R? Explain your answer.

Answer: Line 2. Animal R feeds on Animal Q. Hence, when the population of Animal Q decreases, Animal R have less food to feed on, causing some of them to die of starvation. The population of Animal R decreases.

 

 

Common mistakes

 

Wrong answers: Animal Q feeds on Animal R.

Teachers’ comments: The direction of the arrows in the food chain does not mean that P eats Q and that Q eats R. Instead, the arrows show the direction of the flow of energy. Energy flows from the prey to the predator when the prey is eaten by the predator. Hence, this means that Q eats P and that R eats Q.

 

 

Final note 

Wrong answer: Animal Q is the predator of plant P.

The word “predator” means an animal feeds on another animal.

In the statement above, P is a plant. Hence, you cannot write Q is the predator of the plant.

 

Correct answer: Q feeds on P or P is eaten by Q.

Let’s Try One More Example!

Question

Study the food web below.

An organism that feeds on X is introduced to the habitat. What happens to the population of organism Z?

STEP 1

Identify and explain how the introduction of the organism affects the population of X.

Next, identify and explain how the change in population of X affects the population of Z.

 

FINALLY, put your answer together

An organism that feeds on X is introduced to the habitat. What happens to the population of organism Z?

Answer:

When the organism that feeds on X is introduced, the population size of X decreases. Hence, less X will feed on Z, organism Z will reproduce and the population size of organism Z increases.

 

 

Common mistakes

Wrong answers: Organism X preys on Z. Therefore, population size of organism X increases.

 

Teachers’ comments:

– The answer is unclear as there is a missing link between the two sentences. You need to explain that as the population of X decreases, less X will feed on Z, the population of organism Z increases. A

Also, writing the word “prey” is wrong. Organism Z is most likely a food producer. Why? The arrows are pointing away from Z, indicating Z is eaten by other organisms. The food web most probably begins with the food producer.

The definition of “prey” is when an animal is eaten by another animal. Hence, we cannot write “X preys on Z”.

Instead, write “Organism X feeds on Z.”

You can download this revision notes so your child can revise them anytime.

This will be delivered to your email inbox.

 

✍️You can read the revision notes on living together and energy in food topics.

>>> https://scienceshifu.com/living-together-and-energy-in-food-topics/

(Understand how examiners combine multiple topics into a single question. This is suitable for P6 students.)

Click here for other primary science revision notes >>> https://scienceshifu.com/primary-6-science-revision-notes/

P3 P4 Science GuideBook

Purchase this P3 P4 Science Revision Guidebook for your child

 

Included inside this ebook:

Over 120 pages of detailed science concepts provided

14 challenging exam-based questions for your child to apply the science concepts.

– Detailed explanation videos of 6 exam-based questions

 

Click on the button below to find out more about this ebook

science lessons for primary school students

Subscribe To Our

Pre-Recorded Science Courses

When you sign up for the Pre-Recorded Courses, your child receives the following:

– Learn the science concepts anytime, anywhere – There are lots of recorded videos and lesson notes to learn and revise the science concepts and answering techniques. Submit the assignments from ScienceShifu and our team of science specialists will mark and reply in 3 to 4 days’ time. 

– 24/7 homework helper – Simply take a picture of the question that your child is unsure of and Whatsapp our homework helpline. Our team of science specialists will reply within 1 day.

 

Click on the button below to find out more about our pre-recorded courses

Enrol your child to

the All-In-One ‘Eureka!’ Program

When you sign up for the All-In-One ‘Eureka!’ Program, your child receives the following:

  • Live Zoom Classes conducted by our passionate teachers.
  • EdaptIQ™ – a smart digital assessment book (An adaptive learning platform to customise quizzes and practices to suit your child’s strengths and weaknesses. We have thousands of exam-based MCQs for your child to practise).
  • 24/7 homework help – Simply take a picture of the question that your child is unsure of and Whatsapp our homework helpline. Our team of science specialists will reply within 1 day.

 

Click on the button below to find out more about our program

Join the ScienceShifu Channel to get the latest learning tips.

 

Benefits of joining ScienceShifu on Telegram:

– Be the first to receive science revision notes from us

– Receive special promotions on all our online courses. 

 

Click on the button below to join the ScienceShifu channel:

Follow the ScienceShifu Instagram Channel to learn more science concepts

 

Benefits of joining Instagram:

– Watch out for interesting posts from ScienceShifu explaining science concepts

– Short videos where I will be going through past year exam questions

 

Click on the button below to follow the ScienceShifu Instagram Channel:

Talk again soon!

Andy Ling – Founder of ScienceShifu.com

Guiding your child to be the master of science concepts

 

Download our free revision notes to help your child prepare for the crucial exams.

Be part of our mailing list to receive the latest offers and learning tips from us.

Leave a Reply

Your email address will not be published. Required fields are marked *

*