CELL STRUCTURES AND FUNCTIONS Summarized Biology Notes

This Should Take you About 5 Hours To Study, But Don't Worry If It Takes You More Than Expected, We All Learn At A Different Pace.

WHAT ARE CELLS?

Every living organism is made up of a single cell (unicellular) or many cells (multicellular), all types of cells have certain structures in common such as genetic material and a plasma membrane. A cell can be defined as the smallest biological unit that possesses all the characteristics of living condition. The are different types of cells which includes prokaryotic (lacks nucleus) and eukaryotic (have nucleus) cells such as plant and animal cells. The size of a cell range from millimetre to microns it goes with the definition hence 'smallets' , their sizes also depends on the type of function it performs. Cells do vary in their shapes they can be spherical, rod-shaped, flat, concave, curved, rectangular, oval shape and forth. Unfortunately we can only see cells under a Microscope.

Since both plants and animals are living organisms, they are made up of cells, just like your house which is made up of bricks, the body of plants or animals is made up of cells acting as bricks too. Leaves, Stem, Roots, Flowers, Seeds and The Fruits are all made up of cells in plants. In animals the Skin, Bones, Muscles, Brains and Blood are also made up of cells, now this animal and plants cells have some things in common but not entirely all and some might be present in large numbers in animals whereas a few in plants, for instance plant cells have chloroplasts while animal cells have no chloroplasts, Down We'll look at the features both plant and animal cells have in common 

COMMON FEATURES SHARED BY PLANT AND ANIMAL CELLS

Animal and Plant cells have certain stin common, all cells have a cell membrane, around the outside of the cell contents, inside the cell is a substance known as cytoplasm, containing many small structures called cell organelles for example the nucleus Is a cell organelle, down I'll share the structures shared both by plant and animal cells

• The cell membrane: a thin layer on the surface of every living cell that controls what enters and what leaves the cell

• The cytoplasm: a mixture of proteins and other substances in water that makes up the bulk of every cell

• The nucleus: the structure in the cytoplasm that contains the chromosomes and is surrounded by a nuclear membrane

• Vacuoles: these are contained in the cytoplasm, they generally are larger and fewer in number in plant cells than in animal cells, plant cells have permanent vacuoles. Next are cells images with labelled parts seen through a light microscope 

You need to be able to identify the structures of a plant cell common is the palisade cell, down I'll link images of a plant (palisade) and animal ( human liver) cell, you can cover up the labels of each cell diagram and see how many you can remember, try drawing the cells from memory, use a sharp pencil and add labelled lines to your drawing using a ruler and pen, make sure the labels touch the intended pcross over any other line, write the labels from memory,

PLANT CELL (Palisade cell)

All plant cells are surrounded by a tough, protective layer made up of cellulose that forms a strong cell wall just outside the cell membrane 

ANIMAL CELL (A human liver)

We use a human liver as an example mostly as it's most accurate

LET'S LOOK AT THE FUNCTIONS OF THE STRUCTURES OF PLANT AND ANIMAL CELLS

Each cell type has it's own function, it's the not just to fill up space but for a purpose or else it wouldn't be there, down we'll list the most important cell structures you should learn at your level and their functions. Remember that structure and function are linked together, below we'll look at how the following organelles is related to their structure, they are commonly seven.

1) CELL MEMBRANE

This forms a thin layer around each cell and controls what substances pass in and out of the cell, it's also partially permeable so it allows small molecules to pass through it but not large molecules like starch, the receptors on it's surface enable it to recognise each cell

2) CYTOPLASM

This is a clear, watery, jelly-like substance, it have many substances such as proteins dissolved in it, chemical reactions which are called metabolic reactions take place here

3) NUCLEUS

This is a small body of protoplasm that floats in the cytoplasm it's surrounded by a nuclear membrane, it's responsible for controlling all activities in a cell, it also passes genetic information to produce an exact copy of the cell during cell division. Since it contains chromosomes which are long thread-like structures made of DNA (deoxyribonucleic acid) this DNA contains coded instructions that determine what substances the cell will produce

4) VACUOLE

This are spaces of varying in the cytoplasm of the cell, they are surrounded by a membrane called a Tonoplast which controls entry to and from the vacuole. Larger vacuoles which are found in plant cells store solutions of sugars, salts, pigments and waste, they also provide turgor in a plant cell, Whereas smaller vacuoles found in animal cells are consist of water or solutions of food in animal cells

5) CELL WALL

This is found in plant cells only, they surround the cell which protects and supports the cell as it's made up of very strong cellulose fibres, large molecules are able to pass through the cellulose cell wall, which means it is fully permeable it also prevents the cell from bursting when fully turgid

6) CHLOROPLASTS

Just like a cell wall chloroplasts are only found in green plants cells, they contain a green pigment called chlorophyll which traps energy from the sun to make food for the plant in the process called photosynthesis, strach grains are sometimes visible in chloroplasts

7) MITOCHONDRIA

This are present in all cells, inside the mitochondria energy is released from food during the process of respiration, the number of mitochondria in a cell indicates how active the cell is for example a muscle cell will have more mitochondria than a bone cell.

FUNCTION OF THE STRUCTURES IN THE CYTOPLASM OF AN EUKARYOTIC CELL

The cytoplasm of every cell contains various cell organelles, the number and type of organelles varies from one cell to another, each type of organelle have it's own specific function which it carries out under the control of the nucleus, below are the images I linked, refer to them while reading about this parts

PLANT CELL

ANIMAL CELL

{THE ENDOPLASMIC RETICULUM}

If you closely pair attention to both the cells above you'll notice the two types of endoplasmic reticulum (ER), an endoplasmic reticulum is a network of parallel membranes that form tunnels through the cytoplasm, these tunnels go from the nuclear envelope to the surface membrane, if you look at an micrograph you won't see it as the tunnels do not go directly across at one level, instead they loop up and down in and out through the cytoplasm forming a very extensive system of membranes, all this twisting will then provide a very big surface for the ribosomes to attach to. The are two types of endoplasmic reticulums, Rough endoplasmic reticulum which has ribosomes attached to it's outer surfaces and the Smooth endoplasmic reticulum that does not have ribosomes attached to it

FUNCTIONS OF THE ROUGH ENDOPLASMIC RETICULUM

• transport RNA from the nucleus to the ribosomes

• provide a large surface area for the attachment of ribosomes

• provide transport for proteins through vesicles that the ribosomes produce to the Golgi body or rest of the cell

• be responsible for protein synthesis using ribosomes

If you are closely following you'll realise most of the functions listed above are about ribosomes, you might be wondering what ribosomes are? We'll summarise ribosomes below, ribosomes are very small beads of RNA (rebonucleic acid)

• they are made in the nucleolus of the nucleus

• they move from the nucleus to the cytoplasm

• they attach themselves to the surface of the endoplasmic reticulum

• once attached, they make proteins both for the cells itself and for export to other cells

Below image shows the action of ribosomes

Proteins made by this ribosomes are:

• Pushed through the ER membrane into the tunnels of the ER

• Enclosed in bits of the smooth ER membrane, which then get pinched off to form small transport vesicles

• then carried by these transport vesicles through the cytoplasm to the Golgi bodies

FUNCTIONS OF THE SMOOTH ENDOPLASMIC RETICULUM

• Synthesis of lipids and hormones

• transport lipids and steroids

{THE MITOCHONDRIA}

Mitochondria are easy to identify, they are rod-shaped and are separated from the cytoplasm by a double membrane, the inner membrane has many folds called cristae (one: crista), the crista produce a large surface area for which enzymes attach tool. The inside of the mitochondrion is called the matrix and is filled with fluid, mitochondria break down food molecules mainly glucose which release energy during respiration producing Adenosine triphosphate (ATP). As we mentioned before some cells have many mitochondria while others have few or none, for example muscle cells are always active, no job can be done without using muscles therefore they have lots of mitochondria, nerve cells that transmit nerve impulses don't need a lot of energy therefore they don't need many mitochondria thus the number of mitochondrians in their cells are relatively few. Note that if a cell is not getting enough energy to survive more mitochondria can be produced, sometimes a mitochondria can grow larger or combine with other mitochondria, it depends on the needs of a cell.

THE STRUCTURAL DIFFERENCES BETWEEN TYPICAL PLANT AND ANIMAL CELLS

• Plant cells have cellulose cell walls whereas animal cells have no cellulose cell walls

• Plant cells have chloroplasts with chlorophyll whereas animal cells have no chloroplasts with chlorophyll

• Plant cells have a large vacuole with cell sap while animal cells have a number of small vacuoles or sometimes no vacuole at all

• Plant cells have regular shapes (due to the help of a cell wall presence) while animal cells have irregular shapes (due to the absence of a cell wall)

• Plant cells have a small number of mitochondria whereas animal cells have a larger number of mitochondrians

THE END! FOLLOW THE @BIOLOGISEDTEAMBLOG FOR MORE. Posted By Mr James C.