Science RevisionD.G. Mackean Pages 6-10

Christopher Caden

Cell Specialisation

After a cell divides it has the potential to become specialised. This means that the cell will take on one particular job, a distinctive shape will be formed and new and special kinds of chemical reactions can now take place in the cytoplasm. The new shape and ability to allow new chemical reactions happen means that the cell can take on a specific, specialised role.

Specialised Cells

Ciliated Cells (Found more in animals)

• Forms the lining of the nose and windpipe.

• Tiny cytoplasmic hairs are celled cilia.

• The cilia constantly flick in a wave like motion.

• This motion will carry mucus to the nose away from the lungs.

• The mucus will trap and hold bacteria and dust in it.

Nerve Cells (Found only in animals)

• Conducts electrical impulses.

• “Wired” all around the body and they lead to the brain.

• Some are very long and groups connect body parts like the foot to the spinal cord.

• Chemical reactions allow electrical impulses to travel through the nerve fibre.

• When you tap your knee or arm the nerve cells notice this and sends messages to the brain.

Root Hair Cells (Found only in plants)

• Absorbs water and minerals from the soil.

• The finger like projection increases the surface area and the rate of absorption.

• The cell membrane controls what substances enter and do not enter the cell.

• In the thousands a massive surface area is created and they form the outside layer of roots.

White Blood Cells (Found only in animals)

• Found in the blood stream with red blood cells.

• One function of the white blood cell is to engulf and digest bad bacteria.

• Is flexible and can change its shape.

• Can move into other tissues and go through the blood vessel.

Phloem Cells (Found only in plants)

• The phloem cell transports food in plants.

• They are long cells and join end to end.

• When they meet a wall separates the cells, but the wall has holes in it.

• It is believed that the cytoplasm's communicate to one another and food is passed through the tiny walls.

• The tiny walls are called sieve plates.

Please note!

• This is in no way a complete list.

• There are lots of other specialised cells out there.

Survival of cells.

There are lots of single cell organisms that carry out all the process they need to in order to live. This is not the case for large animals and plants as many of the cells left on their own would die. This is because the cells help one another in the body. For example a muscle cell can’t get its own oxygen or food so on it’s own it would die.

Tissues

There are many different types of tissues. You have bone, nerve and muscle in animals and epidermis, phloem and pith in plants. They are all made up of hundreds of cells with little variation between the cells, in regards to both structure and function. This results in a tissue that has one main task. For example the phloem transports food. There are various ways in how tissues can form and the main ones are listed and explained in the following slides.

Epithelial Tissue

• A thin layer of tissue which usually lies on top of other tissues or organs.

• They protect said tissues from physical or chemical damage.

• There are different types of epithelial tissues.

• Some examples of epithelial tissue in humans are:

• In the mouth.

• Windpipe

• Food canal

Muscle Tissues

• In muscle tissue you can also expect to find other types of cells like blood vessels and nerves.

• They are formed like a sheet and are elastic like so they can easily go back into place after being stretched.

• They are not found just in the arms or legs. Muscles can be found elsewhere, for example in the stomach muscle movement will crush food.

The glands and tubes

• Glands are ball like structures that secrete chemicals and hormones.

• One example of this is the salivary gland.

• After these glands have secreted what they need to the product is carried in small tubes to other organs in the body.

Organs

• Organs are simply a group of tissues working together in unison with one task or goal in mind. They have special functions and there are lots of examples in humans. For example the stomach has epithelial tissue, gland cells and muscle tissues, and the stomach is provided with food and oxygen by the blood stream. The organs do not stop there. The heart, lungs, eyes, brain and intestines are all examples of organs in the human body. Plants also have organs and the main ones are the root, stem and leaves. The tissues that make up the leaf are the epidermis, palisade tissue, spongey tissue and the phloem and xylem.

Systems and Organisms.

Systems are larger than organs, they are organs that work together that have similar functions and goals. For example the nervous system is made up of the brain, spinal cord and nerves. In humans you also have the skeletal and circulatory systems and in plants you have the shoot made up of the stem, leaves and buds. An organism is a created when you have organs and systems working together to make an independent, living thing.

Tissues

Cells

Organs

Systems

Organisms

Tissue Culture

There is a scientific technique called tissue culture and this is where you get a single cell in a dish and the cell divides and a one cell thick tissue is formed on the bottom of the dish. The cells do not become specialised. This is done so drugs and medicines can be tested on the cells to look for any possible harmful impacts of a drug. Another reason this may be done is so scientists can examine and explore how cells divide and learn more about cells and cell division.

Mammal cells usually stop dividing after 20 generations or so.

Practical Work with Plant Cells.

When you want to look at a plant’s cell you usually take a sample from the epidermal tissue which is on the outside of the plant and rhubarb or onions are particularly good when it comes to this. The sample will be soaked with weak iodine and this will stain the nucleus yellow and the starch grains will be blue. If you used the epidermis of rhubarb the cell sap in the vacuole should be seen as a red colour. To see chloroplasts you need to carefully pull a leaf from a moss plant and once that leaf is soaked in water you should see the chloroplasts, however you do need a powerful microscope.

Practical Work with Animal Cells

There used to be a few ways to quickly get animal cells to examine in the classroom and they were, from us. A previous practice involved getting cheek cells from a human and examining the cell, however this was banned due to the threat it posed to spreading AIDS, even though the threat was very minimal. Today there are two ways could get animal cells. The first method is you swabbing your cheeks and gums with a cotton bud and after a through cleaning and after placing some methylene blue solution on the cells you should be able to view them. The second method involves sellotape being put onto a washed wrist, peeled off, and then examined. You should be able to see the cells and maybe a nucleus and putting the same methylene blue solution onto the cells you should be able to see a stained nucleus.

Definitions

• Mammals – Warm blooded animals which have hair on their skin and the women can produce milk for their children.