Primay 5 Science: Cell

I teach science at home with the 2 books above only. That's what he had learnt today.

Cell – smallest unit of life. It is a able to grow, take in food, reproduce and respond to changes in the environment.

Cells come in different shapes, sizes and structures to suit their specialized functions.

The simplest living organisms have only one cell (unicellular) or single-celled, e.g. bacteria, yeast, paramecium, amoeba, euglena.

Organisms made of many cells are called multicellular organisms.

Cell -> Tissue -> Organ -> Systems

An animal cell has a nucleus, cytoplasm, cell membrane and vacuole (they are small if present). It has no chloroplasts and cell wall.

A plant cell has a nucleus, cytoplasm, cell membrane, vacuole, chloroplasts and cell wall.

Not all plant cells contain chloroplast (e.g. root cells & onion skin cells). Plant cells that are not green do not contain chloroplast.

Not all cells contain a nucleus (e.g. human or mammals red blood cells). Red blood cells have the shape of biconcave lens and have no nucleus. Without a nucleus, these cells cannot reproduce and will die eventually. Red blood cells are produced by the bone marrow. In the other vertebrates (e.g. fish, amphibians, reptiles and birds), red blood cells have a nucleus.

Cytoplasm is a jelly-like substance that contains many cell parts. It allows substances to move around within the cell. Many activities of the cell take place in it. It fills the cell.

Nucleus is a round or oval cell part inside the cytoplasm. It controls everything that happens inside the cell. It contains information that is passed on from one generation to another, e.g. DNA.

Cell membrane is a thin layer that surrounds the cytoplasm. It controls the movement of materials going into and out of the cell. A thin layer around the cell also known as plasma membrane. A partially-permeable layer that controls the movement of substances in and out of the cell. It holds the cytoplasm inside the cell.

Vacuole is a tiny space containing air, liquid or food particles. It was found in cytoplasm and it is small and numerous.

In the plant cell, the vacuole is a large space filled with a liquid called cell sap. Cell sap contains water and dissolved substances like sugar and salt. Cell sap makes the plant cell firm. The central space of the plant cell may be occupied by a large, single vacuole.

Cell wall is a stiff layer around the cell membrane. It supports and gives the plant cell its shape. It is made up of a tough material called cellulose.

Chloroplast is a tiny disc-like cell part that contains a green pigment called chlorophyll. It captures sunlight for plants to make food.

Cells increase in number by a process called cell division.

A cell went through cell division and produced two “daughter cells”.

New cells are produced to replace dead or damaged cells.

Cell division enables organisms to grow and reproduce.

All unicellular and multicellular organisms undergo cell division.

Cell division in yeast. Parent cells form smaller daughter cells by a process called budding.

Both growth and reproduction involve cell division.

Growth is the irreversible increase in mass that results from cell division (number) and cell expansion (size).

Our body comprises trillions of cells.

White blood cells help our body to fight infection.

Red blood cells carry oxygen to all parts of our body. The average life cycle of a red blood cell is 120 days.

Brain cells are nerve cells that process and transmit information through the nervous system.

Most cells are very small and can only be seen under the microscope. The chicken egg cell is an exception; it is one big cell- large enough for breakfast. The largest known cell is an ostrich egg.

Good to know:

An antibiotic is a “poison” that works to destroy bacterial cells while leaving human cells unharmed. The life of a cell is dependent on the enzymes that float in the cell’s cytoplasm. All antibiotics take advantage of the fact that there are many differences between the enzymes inside a human cell and the enzymes inside a bacterium.

Penicilin was one of the first antibiotic. It gums up a bacterium’s ability to build cell walls. Since bacterial cell walls and human cell walls are very different, penicillin has a big effect on certain species of bacteria but no effect on human cells. The sulfa drugs work by disabling an enzyme that manages the creation of nucleotides in bacteria but not in humans. Without nucleotides, the bacteria cannot reproduce.

You can see that search for new antibiotic occurs down at the enzyme level, hunting for differences between the enzymes in human and bacterial cells that can be exploited to kill bacteria without affecting human cells.

The unfortunate problem with any antibiotic is that it becomes ineffective over time. Bacteria reproduce so quickly that the probability for mutation is high. In your body, there may be millions of bacterial that antibiotic kills. But if just one of them has a mutation that makes it immune to the antibiotic, that one cell can reproduce quickly and then spread to other people. Most bacterial diseases have become immune to some or all of the antibiotics used against them through this process.

Antibiotics do not work on viruses because viruses are not alive. A bacterium is a living, reproducing life form. A virus is just a piece of DNA. A virus injects its DNA into a living cell and causes that cell to reproduce more of the viral DNA. With a virus, there is nothing to “kill”, so antibiotics do not work on it.

Extra Information:

I often use encyclopedia to make the teaching fun too. We all should have one good encyclopedia at home. I bought it at S$25 online. :)