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4.Cell structure and organization

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CELL STRUCTURE AND ORGANIZATION

The Cell is a basic unit of life.

  • All living things are composed of cells which called carry out the process that make the organism lives entity.
  • All cells are basically the same in chemical composition. All life processes take place in the cells.
  • Some organisms are made up of many cells and are called multi cellular organisms e.g. man, pine tree, locust.
  • All cells are microscopic, its membrane bound it has structures that are site for chemical reaction called organism.
  • They have ability to replicate, since they contain the genetic materials. So these are characteristics of cell.

TYPES OF CELLS

These are two basic types of cells

  • Prokaryotic cells
  • Eukaryotic cells

Prokaryotic cells are found in organism which they do not have membrane bound organelles, they do not have nucleus.Prokaryotesare mostly single celled organisms such us bacteria and blue green bacteria.

Eukaryotic cell are cell which they have a membrane bound nucleus. They contain specialized membrane bound organellesEukaryoticcells can be found in a single celled organism such as Amoeba or they found in multi cellular organisms.


 ANIMAL AND PLANT CELLS Both animal and plants differ in structure and function in order to be able to meet the requirements of each organism.

Plant cell


Animal cell

FUNCTION OF THE PARTS OF ANIMAL CELLS

  • CELL MEMBRANE
  • Is also known as plasma membrane or plasma lemma.
  • Is thin layer that encloses the whole cell

Function of cell membrane

  • Communicate with other cells.
  • It allows selective movement of substances into and out of the cell. It is said to be a selectively permeable membrane or differential membrane
  • It encloses the contents of the cell
  • CYTOPLASM
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This is jell like substance made up of water and dissolved chemical substances. The cytoplasm is the site for many chemical reactions in the cell. Cell organelles such as the vacuoles, nucleus and mitochondria are suspended in the cytoplasm. The movement of cytoplasm is known as cytoplasmic stream

  • NUCLEUS

This is a round or oval organelle suspended in the cytoplasm. The nucleus is made up of nucleolus and fluid called nucleoplasma. It’s surrounded by a membrane called the nuclear membrane.
Functions of nucleus

  • To determine the chemical processed that take place in the cell.
  • To control the functions of all parts of the cell
  • To determine the cell’s size, shape and function
  • To determine the hereditary characteristic of a cell
  • VACUOLES

Cell vacuoles are fluid filled spaces bound by a membrane. Animal cells have small and temporary vacuoles mainly used to secret and excrete wastes from the cell.

  • MITOCHONDRION

Is a sausage – shaped (oval shaped) organelle. A mitochondrion is bound by two membranes namely: –

  • Outer membrane
  • Inner membrane

The inner membrane is greatly folded into cristae to increase the surface area for cellular respiration.The fluid in which cellular respiration takes place in the mitochondrion is called matrix. The function of mitochondrion is the site for respiration, reactions which yield energy for the cell.

STRUCTURE OF MITOCHONDRION

  • CENTRIOLES

Centrioles are rod shaped cylindrical structures located just outside the nuclear membrane.During cell division they move to opposite sides of the nucleus to form the ends of the spindle.


Function of centrioles They take part in cell division and also in the formation of alia and flagelli in cells where these structured are present.

  • LYSOSOMES

Lysosomes are membrane bound sacs within the cytoplasm of animal cells

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Function of Lysosomes They contain enzymes responsible for the digestion of materials in food vacuole. They destroy worn out organelles within the cell.They may sometime destroy the entire cell.


Function of parts of plant cells

1. CELL WALL

  • This is a strong covering made of cellulose.
  • The cell wall is fully permeable. It allows the passage of water and minerals, gases (freely permeable).
  • Protects and gives the cell a definite shape         

     2.CHLOROPLAST

  • They are sites of photosynthesis
  • It Contain green pigment called chlorophyll.
  • Chlorophyll absorbs the light energy needed for photosynthesis

3. VACUOLE Vacuoles maintain a balance between water molecules and solute molecules in the cell; contain color pigments, which give color to flower.The fluid inside vacuole is known as cell sap


SIMILARITIES BETWEEN PLANT AND ANIMAL CELL

  • Both have cell membrane
  • Both have cytoplasm
  • Both have nucleus
  • Both have vacuoles, ribosome and mitochondrial

Differences between plant cell and animal cell

Plant cellAnimal cell
Has a cell wallNo cell wall
Has chloroplastLacks chloroplast
Have definite shapeHave no definite shape
Has a large permanent vacuoleHas small temporary vacuole
They are normally largeThey are usually smaller
They stores oil, proteins, starchThey store fats and glycogen

 CELL DIFFERENTIATION

  • Cells have different functions and features that make them better suited to carry out these functions. This is called cell differentiation.
  • Most living things are made up of many structurally and physiologically adapted different kinds of cells.
  • These cells perform specific function and this is referred to as cell specialization.
  • Cell differentiation refers to the way cells are adapted so that they can carry out function efficiently.
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TISSUEA tissue is a group of similar cells performing the same function. Basically there are two types of tissue.Animal tissue e.g. epithelial tissue, muscular tissue, blood tissue, nerve tissue, skin tissue.Plant tissue e.g. meristematic tissue, parenchyma tissue, collenchyma tissue, vascular tissue, xylem tissue, phloem tissue


ORGAN An organ is a functional unit formed by a group of specialized tissue.

Animal organ:       – heart, kidney, liver, brain, tang, stomach

Plant organ:          – roots, leavers, flower, stem

SYSTEM System is made up of organs that work together to perform a certain function.Examples of system are Respiratory system, digestive system, reproductive system, hormonal system, skeletal system and blood circulatory system, nervous system. 


ORGANISM An organism is the individual living organism e.g. Animal and Plant.An organism is made up of different systems working together therefore there is specialTissue

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Importance of cell differentiation

Cell differentiations leads to division of labour.Division of labour means each cell does a specific function. This helps the body to carry outall life processes at the same time and more efficiently.To achieve this, cells must become specialized to carry out special functions.* Study more about specialized cell for different function e.g.

White blood cell (WBC) can change their shape to engulf and destroy harmful pathogen.

Red blood cell (RBC) for transporting oxygen (they are biconcave and lack nucleus)

Sperm cell – Fertilizes the female egg (have tails for swim pointed head for easy penetration)

Root hair cells – for absorb water and mineral salts (have extended portion helps to increase surface area for absorption)

Guard cell – control open and close of stomach (the inner wall is thinker than outer)

Palisade cell – makes it to expand irregularly

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