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Being Multicellular

What are the advantages of having lots of cells?

If you want to be bigger than an Amoeba you need either giant cells or lots of cells. As the SA:Vol ratio limits cell size the only option is to be an organism made from lots of cells. The human body contains trillions of cells. This activity is about the characteristics of living things, cell differentiation and the complexity that emerges from simple cells joining together to make organs, emergent properties. A series of video clips and questions lead students to understand the main concepts and make a few notes.

Lesson Description

Guiding Questions

What are the characteristics which all living things have, always?

How can you make big animals, or plants when cells are limited in size by the SA to Vol ratio?

Can new characteristics or new properties appear when many cells live together?

Activity 1 The characteristics of living things

One of the most famous single-celled organisms is the amoeba. Watch the two videos below then answer the questions on the Being Multicellular student worksheet

A single celled amoeba engulfs two single celled animals

The Characteristics of living things - using the acronym "Mrs H. Gren"

This is a great 60 second review of the characteristics of living things.

Questions about unicellular organisms

  1. How do you think an amoeba can be "sensitive" to its environment?

    Hint: It can't have specialised cells forming sense organs.

  2. What substances in the amoeba may be kept in a constant state by homeostasis?

    Hint: What are the needs of the cell?

  3. What you have just seen in the amoeba is a good example of nutrition, how does excretion happen?
     
  4. How many of the characteristics of living things do humans and amoebas share?

Students can use the  Being Multicellular student worksheet

Activity 2 What happens when one cell divides to make a multicellular organism?

If you want to be bigger than an Amoeba you really have to be multicellular.
What happens as groups of cells grow? Do any new properties emerge?

Watch the videos below then describe the process of differentiation and the emergence of new properties when many cells work together. These properties could not exist in a single celled organism like an amoeba.

From embryo to fetus - becoming multicellular

Start watching from 1min30s

Human embryo development - focus on cells

This video shows how the cells differentiate during early embryo development.

Making a Human - Simple Science (Nature magazine)

This is an excellent interview with an MIT professor. It could make an activity in itself.

Questions about multicellular organisms.

  1. Name four different types of specialist cells which a single celled human zygote can differentiate into.
    What makes them different from each other?
     
  2. Suggest a property of one of these groups of specialist cells which could not exist if there were not a large umber of cells living together?
     
  3. It is said that thoughts we have in our brains is an emergent property. Explain why this is 'emergent'.

Teachers notes

This topic is important as a link between the study of cells and the study of larger organisms like humans. The appearance of emergent properties has inspired the relatively new field of systems biology. We could not learn all there is to know about the human body by studying cells on their own.

There are two short activities where students watch films and answer questions.

The activity should take about 50 minutes. It can be delivered to students as a teacher led discussion or it can be set as an independent activity using the Student access.

Model answers with filtered student access can be found here: Being multicellular - model answers 

There is plenty of opportunity for extension work,

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