Cells and their functions

Humans are multi-cellular animals. That means we are made of lots of cells, not just one cell. The cells in many multi-cellular animals and plants arespecialised, so that they can share out the processes of life. They work together like a team to support the different processes in an organism.

Specialised cells

You should be able to work out special features of a cell from a drawing, if you are told what the cell can do. The tables below show examples of some specialised animal and plant cells, with their functions and special features.

Type of animal cell	Function
Red blood cells	To carry oxygen
Nerve cells	To carry nerve impulses to different parts of the body
Female reproductive cell (egg cell)	To join with male cell, and then to provide food for the new cell that's been formed
Male reproductive cell (sperm cell)	To reach female cell, and join with it

Type of plant cell	Function
Root hair cell	To absorb water and minerals
Leaf cell	To absorb sunlight for photosynthesis

Animal cell

Even if you're just studying, a lot of work is going on in your cells. Let's zoom down and check it out.

Membrane

We've arrived in the space between two cells.  A sticky coat called the extracellular matrix holds the cells together. Each cell is surrounded by a flexible plasma membrane with an incredible number of projections, docking stations, and channels. Let's dive into one of these channels to enter a cell.

Cytoskeleton

Wow! Look at this place! These girdles and cables make up the cytoskeleton, the structural framework of the cell. They also serve as tracks for transporting cargo from one place to another.

Mitochondria

All this activity in the cell requires energy, in the form of ATP molecules, which are made here, in the mitochondrion. Notice the outer membrane and the inner membrane, with its numerous infoldings. Many of the molecules involved in making ATP are built into the inner membrane. All those folds increase the inner surface area, enabling more ATP to be made.

Nucleus and Ribosomes

Moving towards the nucleus we pass by layers of internal membranes. The nucleus is enclosed by a double membrane called the nuclear envelope. Let's enter the nucleus through a pore.

The nucleus houses the genetic material of the cell, DNA, which carries the blueprints for making the cell's proteins. Almost two meters of DNA is crammed inside the nucleus. How does it all fit?! The DNA is wrapped around proteins like thread wrapped around spools.

Look! This section of the DNA has unwound, and a different protein has attached to the DNA. DNA is being used as a template to make mRNA. mRNA molecules travel from the nucleus to the cytoplasm, carrying the instructions for making specific proteins.

In the cytoplasm, a ribosome clamps onto a strand of mRNA. The ribosome ratchets along the mRNA, building a new protein. Some proteins stay in the cytoplasm; others, like this one, are processed in special compartments within the cell.

Endomembrane System

Protein processing and certain other metabolic activities occur in the endomembrane system, the cell's network of internal membranes. The endoplasmic reticulum, or ER, is part of the endomembrane system.

There are two types of ER: rough and smooth. Rough ER is covered with ribosomes. Smooth ER lacks ribosomes. Lipids are made in the smooth ER. Let's go inside the rough ER.

Note that you can still see the ribosome in the outside surface. The ribosome is manufacturing a new protein., which continues to grow inside the ER. Completed proteins move to the edge of the rough ER, and depart in a vesicle that buds off from the ER membrane.

Some vesicles fuse with the Golgi apparatus, another component of the endomembrane system. In the Golgi, proteins undergo further processing. Finished proteins are packaged in vesicles that pinch off from the Golgi and are transported along cytoskeleton tracks.

Some vesicles bind with the plasma membrane, secreting their contents outside the cell. Other vesicles, called lisosomes, contain digestive enzimes. Here, a lisosome fuses with a worn-out mitochondrion and breaks it down.

Each of the trillions of cells in your body is a dynamo of activity, requiring millions of ATP every minute. But most people are unaware of all this activity in their cells.

Plant cell

A) Videoclip projection: Plant cell

PLANT CELL

   Both animals and plants are made up of cells. Their cells have many features in common, but there are a few significant differences. Let's look inside a leaf to take a closer look at a plant cell.

         Cell Wall

    First, we encounter a protective cell wall outside the plasma membrane. The cell wall is made from strong cellulose fibres.

         Central Vacuole

   Once inside the plant cell, we see the large central vacuole, which regulates the composition of the cytoplasm, creates the internal pressure that is characteristic of plant cells, and stores various compounds produced by the cell.

         Chloroplasts

   Plants make their own food by photosynthesis in chloroplasts. Light passes through the two membranes of the chloroplast and strikes these green disks, where light energy is converted to chemical energy.

The sugar molecules produced by photosynthesis can be made into other molecules or broken down for energy.

         Mitochondria

   All plant cells have mitochondria, just like animal cells do. Sugars produced by photosynthesis are broken down and converted to ATP in mitochondria. Most organelles, like mitochondria, are found in both plant cells and animal cells.

So, the next time you pass by a plant, remember that we have more in common than meets the eye.

Radiation

Activity: The radiation spectrum

https://www.youtube.com/watch?v=hPJPbbT1TsM

The story so far...

One of the chief ways in which heat energy moves is in the form of waves. Sources of heat, such as the sun or a fire or a stove, send out these waves in all directions, as if each wave where the "spoke" or - to use the Latin word - the radius of a wheel. This is why this third kind of heat transfer is called radiation.

And now...

The radiation spectrum

In warm weather, you seem to feel hotter if you're wearing black than if you're wearing white. Is this just your imagination, or are black things really warmer than white things? What could colour have to do with heat? What is colour, anyway? Why are tomatoes red? Or oranges orange? Or buttercups yellow? Or green beans green? Or blueberries blue? Or violets violet? Where do all these colours come from? 

They come from light itself. White light contains all the colours. See for yourself. Go into a dark room. Open a chink in the blinds, and let a narrow beam of light in. Now hold a glass prism in the light beam. Look at the colours: red, orange, yellow, green, blue, violet. That's what white light's made of.

When it shines all these colours on a tomato, the tomato absorbs each of the colours - except red, which it reflects; that's why tomatoes look red. 

Oranges do the same. They absorb all the colours - except orange, which they reflect; so oranges look orange. 

Buttercups only reflect yellow, so they look yellow. The same thing applies to green beans... blueberries... and violets. 

Now if you mix all these colours together again you get white light once more, because white is simply a combination of all the colours. 

Your white suit appears white because it doesn't absorb any of the colours - it reflects them all. On the other hand, your black suit appears black because it absorbs all the colours. It doesn't reflect any of them. Black is simply the absence of any colour.

But what's all this got to do with black being warm, and white being cool?

Well, when the sun radiates waves of heat energy, these waves come in many different forms, which make up a whole band, or spectrum, of energy waves, from radio waves at one end, to x-rays and gamma rays at the other.

Some of this heat energy is visible. These are the light waves made up of all the different colours. But these only take up a little bit of the radiation spectrum. The rest of the spectrum isn't visible at all.

There is, for example, some invisible radiation just beyond, or beneath, the red. Since the Latin word for beneath is "infra", this is called infrared radiation.

Now most of the sun's radiated energy comes to us in the visible and the infrared parts of the spectrum, and that's why black is warm: because it not only absorbs the heat energy of the visible colours, but in doing so it also tends to absorb a lot of the heat energy of the invisible infrared radiation as well.

Conversely, white is cool, because it not only reflects the heat energy of the visible colours, but in doing so it also tends to reflect a lot of heat energy of the invisible infrared radiation.

So now you know that colour really does have something to do with heat - it isn't just your imagination. You also know what lies at the end of the rainbow. It isn't a pot of gold - it's infrared radiation!

Unit 3 Heat and temperature

Read the following text and watch the video

Activities1

Activities2

Activities3

Unit 2 Matter and energy

Matter and energy

Renewable energy sources

The moon and the earth

Make the Earth orbit exactly one around the Sun by setting a number of months and clicking GO

Activities