Part 3: What goes on inside a cell?

Part 3: What goes on inside a cell?Activity 3.1 What’s inside a cell?Activity 3.2 What makes cells function?Activity 3.3 Yeast metabolismActivity 3.4 Cell divisionActivity 3.5 Why are cells so small?

34From Little Things Big Things Grow Student Guide Part 3

PART

3

Cell types

What to do:

Step 1Look at diagrams of the four main types of cells on this page.

Step 2In your Notebook record their similarities and differences.

Step 3Discuss your findings with the class.

Cells come in different shapes and sizes but can usually be classified into one of four groups.

Click here to see cells in more detail.

Hint: • The shape of the cell can give you a

clue. Plant and fungal cells are often box-like. Animal cells have more irregular shapes.

• The cell wall is a structural layer outside the cell membrane that gives the cell structural support and protection. In plants it is made from cellulose, a long chain molecule made from many sugar molecules joined together. In fungi the cell wall is made from chitin; the same hard material that forms crab and lobster exoskeletons. Chitin is similar to cellulose but it contains nitrogen and has added strength. Bacterial cell walls are made from a mesh-like substance called murein, made from sugars and amino acids joined together.

? Are all cells the same inside?

Animal cell

Plant cell

Fungal cell

Bacterial cell

nucleus

cytoplasm

cytoplasm

cell membrane

cell wall (made of murein)

chromosome instead of a

nucleus

cell membrane

small vacuole

nucleus

cytoplasm

cell membrane

cell wall (made of cellulose)

chloroplast

vacuole

cytoplasm

cell membrane

cell wall (made of chitin)

vacuole

nucleus

food storage granule

35From Little Things Big Things Grow Student Guide Part 3 What goes on inside a cell?

Activity type

Activity 3.1 What’s inside a cell? DOWNLOAD e-NOTEBOOK

https://www.sciencebydoing.edu.au/curriculum/student/from-little-things/digital/part3/activity1

https://www.sciencebydoing.edu.au/download/0503010102

Jigsaw activity

For this jigsaw activity, form into groups of four students and assign each student to investigate a different part of the cell:• mitochondria• chloroplasts• nucleus• cell membraneEach student becomes an expert on a different aspect of the cell.Your group then discusses how each part of the cell is important for it to work efficiently.

What to do:

Step 1Your task is to research and understand your cell part. You will

need to explain it to your group, so Notebook as you go.

Step 2After the researching the group comes together and each member takes turns to explain their information. Other members learn about the other three cell parts and take their own notes. A table is a useful way to summarise your findings.

Step 3Together, the group will discuss any connections between the various cell parts. Each member will record any new scientific understanding they gained about how cell parts work together.

Step 4The groups join a class discussion where a representative from each group will present their new understandings.

?How can separate bits of scientific evidence be pulled together to give a bigger picture?

mitochondrion

nucleus cell membrane chloroplast

Did you know that structures with specific jobs in cells (nucleus, chloroplasts, mitochondria) are called

ORGANELLES?

Click here to research your part of the cell.

Cell part Structure (a diagram could help)

Main roles Other information

Mitochondrion

Chloroplast

Nucleus

Cell membrane


Activity type

Activity 3.2 What makes cells function? DOWNLOAD e-NOTEBOOK



What a gas!

What to do:

Step 1Form a group of three or four students.

Step 2Plan your experiment:• what equipment will you need?• how will you set it up?

Step 3Set up the experiment.

Step 4Observe the results over 30 minutes. While you wait, draw a table in your Notebook to show your results clearly.

Yeast is a micro-organism used in baking and in making

alcoholic drinks. To survive and grow, it needs water, sugar and

warmth. It gives off bubbles of carbon dioxide gas as it produces energy; the better

the conditions are for growth, the more gas is produced.

To find out we will do the experiment at three different

temperatures, 20°C, 40°C and 60°C. If we keep all the other

variables the same this will be a controlled experiment.

• What important things should be kept the same?

• How can we do this accurately?

Why is it important to divide the yeast equally?

How will you do this?

How will you measure differences in the

amount of gas produced at each temperature?

How can you collect the gas?

How will you keep the

temperature of the water

constant for each flask?

? Does yeast show the

characteristics of a living thing?

HOW WARM DOES IT NEED TO

BE?


Activity type

Activity 3.3 Yeast metabolism DOWNLOAD e-NOTEBOOK


What to use:

Each GROUP will require:

• microscope• slide and cover slip• eye dropper• tissue• mounted needle or toothpick.

What to do:

Step 1Set up your microscope and ensure the lenses are clean.

Step 2Take one small drop of yeast solution from one of your flasks and place it in the centre of your slide. Which is the best one to choose?

Step 3Carefully lower the cover slip from one side using the mounted needle or toothpick.

Step 4Wipe away excess water on your slide.

Step 5Use the 10X objective lens and coarse focus to look at the yeast cells. They are very small so, once you have them in focus, change to the 40X lens and check the fine focus and light.

Step 6In your Notebook draw a few cells.Can you see any cells that are joined together? If so draw them.

? What does unicellular

mean?

? Into which of

the four types of cells would you classify yeast?

Yeast is a unicellular organism.

All its metabolism occurs in one cell.

When a cell reaches its maximum size, a small piece is divided off to form a new

individual. This is called

BUDDING.

Yeast cells can reproduce

themselves! You can use a microscope

to watch this happen.

Check! Review the details of how to use a microscope in Activities 2.3 to 2.5.

Budding cells

parent cell bud forming new cell

nucleus splits in two

new cell is formed


Activity 3.3 Yeast metabolism Continued

Discussion:

• What evidence is there that a gas is being produced?

• What gas do you think it is? Explain.

• Did the experiment indicate that yeast prefers to live at any particular temperature? Explain.

• Draw a line graph to show the effect of temperature on the amount of gas produced.

• Write a conclusion for this part of the experiment.

What characteristics

of living things did you discover in yeast?

Can you find at least four?You might like to

consult the list of the CHARACTERISTICS

OF LIFE in Activity 1.2.

Hint: What axis

will you use for the temperature

(independent variable)? What axis will you use for

the size of the balloon (dependent variable)?

Hint: Think back to the aim of the

experiment and try to write your answer in

one sentence.A test

for carbon dioxide is that

it turns lime water milky. Your teacher will show you this

test.

How could you

show that yeast produces the same gas?

When we breathe out, a

waste product from our cells (carbon

dioxide), is passed out from our lungs.


Activity 3.3 Yeast metabolism Continued

The algae, Chlamydomonas, has everything it needs to survive in its single cell. It has:• a nucleus to control cell functions• chloroplasts for photosynthesis,• mitochondria for respiration• a cell wall and cell membrane through

which it takes in what it needs and expels as waste what it no longer needs.

What are the two main

reasons for

BINARY FISSION?

Single-celled algae Chlamydomonas divide by BINARY FISSION and separate to produce two identical individuals.

Cells divide by binary fission and do not separate entirely, but form a connected colony of 16 cells.

Antonie van Leeuwenhoek first reported observing Volvox in 1700. Volvox is a pond algae that forms colonies of up to 50,000 cells. The cells form a hollow sphere, one cell thick, with each cell waving a flagellum on the outside of the sphere to keep the colony moving towards the sunlight. Some cells become specialised as reproductive cells on the inside surface of the sphere. They are large and lack flagella and divide several times to form new colonies. Volvox may have been one of the first multicellular organisms. Can you explain why?

? How are new cells

made?

Many other similar organisms exist as colonies of identical cells.

Click here to investigate cell division further.

Volvox

PandorinaChlamydomonas

Gonium


Activity type

Activity 3.4 Cell division DOWNLOAD e-NOTEBOOK



Diffusion into agar blocks

? Actually … some are

bigger.Do you recall larger

cells? How do they get away with it?

WHAT IS DIFFUSION?Diffusion means the movement of particles in solution from a high concentration to a low concentration. Here, the acid particles are in a high concentration in the beaker and move (diffuse) into the agar, where there is no acid. As the acid moves in, it turns the pink indicator clear.

What to use:

Each GROUP will require:

• pink agar cubes with sides of 1 cm, 2 cm and 3 cm

• 0.1 M sulfuric acid (100 mL)• 250 mL beaker• stop watch• knife or scalpel• ruler• paper towel.

Each STUDENT will require:

• safety goggles.

What to do:

Step 1Read the procedure and think about how you will record your results in your Notebook.

Step 2Half fill the beaker with sulfuric acid.

Step 3Carefully lower each agar block into the acid, making sure they do not touch.

Step 4Start the stopwatch when you put the blocks in the acid. The acid in the beaker will diffuse into the agar, turning the pink indicator clear.

Step 5Observe each agar block for 15 minutes. If any turn completely clear, note the time.

Step 6Pour the acid out of the beaker and rinse the blocks well with water.

Step 7Cut each block down the centre into two and measure the length of any remaining pink area.

Emu egg

frog spawn before fertilisation: 2 mm

In this activity you will investigate why cells need to divide and remain small.

Can you design a table? Is this experiment a fair test? Discuss with your classmates.


Activity type

Activity 3.5 Why are cells so small? DOWNLOAD e-NOTEBOOK


Discussion:

1. What happens to the extent of diffusion as the blocks get bigger? Try to explain this. It’s tricky!

2. How does this affect the metabolism of a cell?

3. Not all cells are cubes or spheres. Look at the cells in the lower right of this page. Order them from most to least efficient for diffusion of materials in and out of the cell.

4. Why can some cells, such as eggs, be much larger than other cells?

5. The relationship between surface area and volume can be used to explain many everyday things. Try these!

a. Why is a teabag quite flat rather than spherical?

b. Why are you more likely to get frost-bite on your fingers, toes and ears than on your cheeks?

c. Why do snakes coil up in cold weather?

d. Why are teapots ‘short and stout’?

e. How could you cool down a very hot roast potato quickly?

f. What is a three-dog night?

Why does a three-dog night refer to a very cold night?

As a cube (or cell) gets bigger, the amount of surface (the surface area) compared to what is inside the cell (the volume), gets smaller. This means there is less surface area, in proportion, for diffusion to occur into a greater amount of cytoplasm.Have a look at a tennis ball compared to a basketball to help you see this relationship!


Activity 3.5 Why are cells so small? Continued

43

PART

3Cells can be classified into one of four groups as shown in this table:-

Cells are surrounded by cell membranes. The cell membrane is a flexible membrane that keeps all the cell contents inside. There are tiny holes in the cell membrane that allow molecules to move in and out of the cell.Organelles are tiny cell structures that perform specific cell functions. Some organelles are:-Nucleus – a dark, round spot in the cell that acts as the control centre of the cell. The nucleus controls cell functions like metabolism, movement and reproduction.Mitochondria – long oval structures that take in nutrients (sugars) and create energy-rich molecules for the cell using a chemical process called respiration.Chloroplasts – are only found in plants and algae. They are oval in shape and green in colour because they contain the green pigment chlorophyll. Chloroplasts convert the energy of the sun into sugars using the chemical process called photosynthesis. These sugars can be stored in the plant or used straight away by the cell’s mitochondria.

Single-celled organisms have various methods of feeding. The Paramecium swims with the aid of cilia and sweeps food into its oral groove to make food vacuoles. Euglena swims using its flagellum and absorbs nutrients through its cell membrane. It can also take in sunlight to make sugars in its chloroplasts. The Amoeba engulfs its food with its pseudopods by a process called phagocytosis.

Yeast is a single-celled fungal organism that requires warmth, sugar and water for growth. It produces daughter cells by budding.

Binary fission is the name given to cell division where a single-celled organism, like the algae Chlamydomonas, divides into two smaller, identical cells. Several other algal organisms undergo binary fission but the cells do not separate and they form colonies of cells.

In multicellular organisms the cell division that produces two identical cells is called mitosis. Before mitosis begins each chromosome forms an identical copy of itself. The mitosis process:- • begins when the DNA inside the nucleus begins to

coil up to reveal visible chromosome pairs. • the two centrioles move to opposite sides of the

cell and protein fibres grow to form the spindle. The nuclear membrane around the nucleus disintegrates.

• the chromosomes move to the centre of the cell.• the spindle fibres pull the chromosome pairs apart to

opposite poles.• the chromosomes unwind and nuclear membranes

reform.• the cell separates into two identical daughter cells.

All particles in solution are moving and bouncing off each other. Diffusion is the name given to the process where particles natural jostle from a high concentration to a lower concentration. Cells rely on substances outside the cell (e.g. water, sugar) to diffuse into the cell for cell metabolism. When the cell grows larger it has a relatively larger volume in comparison to its cell surface and the rate of diffusion slows down. To maintain high diffusion rates, cells divide into smaller cells when they get too big.

Cell type Shape Cell components

Animal Round or irregular in shape

Nucleus, cytoplasm, cell membrane and small vacuoles.

Plant Generally box-like Nucleus, cytoplasm, cell membrane and large vacuoles, plus cell wall (cellulose) and chloroplasts.

Fungal Generally box-like Nucleus, cytoplasm, cell membrane and vacuoles, plus cell wall (chitin) and food storage granules.

Bacterial Small and either spherical, rod-shaped or twisted.

Cell wall (murein), cell membrane plus a chromosome in the cytoplasm.


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Part 3: What goes on inside a cell?