CAHPTER 2: CELL STRUCTURE AND CELL ORGANISATION

FIGURE 1: PLANT CELL

Cell Structure and Function

Comparison between Animal Cell (AC) and Plant Cell (PC)

FIGURE 2: ANIMAL CELL

1. Mitochondrion (pl: Mitochondria): AC and PC

• spherical / rod-shaped organelles
• two membranes: Inner membrane – form cristae & Outer membrane – regular and smooth
• an energy source
• site of cellular aerobic respiration
• produces ATP (adenosine triphosphate)

2. Nucleus (pl: Nuclei): AC and PC

• contains the genetic material
• regulates and controls the activities of the cell
• an organelle bounded by double (2) layers of nuclear membrane with pores and selectivelypermeable
• responsible for all cellular structure, chemical functions, growth and reproduction
• separates the genetic materials (chromatin) from cytoplasm

3. Nucleolus: AC and PC

• spherical structure within the nucleus
• consists of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) and proteins
• visible when the cell is not dividing
• synthesis RNA which is needed to make ribosomes

4. Nucleoplasm: AC and PC

• fluid contained within the nucleus
• highly viscous solid
• made up of the chromatin and the nucleolus

5. Chromosomes

• thread-like structures (consists of genetic material)
• appears as chromatin spread throughout the nucleus in the form of tiny granules
• chromatin condenses into chromosomes (during cell division)
• carry genetic information in its DNA

6. Ribosomes: Ac and PC

• small dot-like organelles
• protein synthesis
• consist of RNA (ribonucleic acids)
• smallest cellular organelles
• attached on the surface of ER and occur freely in cytoplasm

7. Endoplasmic reticulum (ER): AC and PC

• connected to the nuclear membrane
• synthesises proteins, steroids and lipids
• collects, stores and distributes protein, steroids and lipids
• exists as rough ER and smooth ER
• Rough ER: covered with ribosomes, flat sealed sac which continued from the nuclear membrane, transports protein, and have a large surface area for chemical reactions.
• Smooth ER: does not have ribosomes, transports lipids and presents in large amounts of cells.

8. Plasma membrane: AC and PC

• cell membrane
• thin membrane surround the cytoplasm of a cell
• selectively permeable / semi permeable
• a protective and selective outer barrier
• consists of phospholipids and protein molecules

9. Golgi apparatus / Golgi body: AC and PC

• bound sacs
• processes, packages and transport molecules synthesised in the cell
• forms lysosomes
• transports and stores lipids
• synthesis of carbohydrate from hormone
• changes protein into glycoprotein
• excretes waste products out of the cell

10. Cytoplasm: AC and PC

• aqueous solution (except nucleus)
• stores water, enzymes, nutrient, salts and dissolved gases
• provided support, shape and protects the cell organelles
• medium for metabolic reactions
• provides substances

11. Lysosome: AC

• sac-like organelle with one membrane
• digest proteins, lipids and carbohydrates
• removes undigested materials
• releases enzymes to digest external materials

12.  Centriole: AC

• are paired cylindrical organelles
• nine tubes with three tubules each
• produces spindle during cell division (mitosis and meiosis)
• migrate to the opposite poles of the cell (during cell division – will be discussed in Chapter 5 Cell Division)

13. Vacuole: AC (temporary / lower class species) and PC

• small cavity in the cytoplasm
• bound by a single membrane
• filled with cell sap
• storage of food (protein, oil and water)
• some vacuoles remove metabolic waste
• functions as cell expansion
• Amoeba: food vacuoles (phagocytosis)
• Paramecium: contractile vacuoles (expel water)

14. Cell Wall: PC

• rigid and tough cellulose layer surrounding the plasma membrane (cell membrane)
• protects and supports the cell
• maintains the shape
• prevents the cell from busting (excessive intake of water)
• allows substances to move freely through the cell wall

15. Chloroplast: PC

• disc / lens-shaped organelle
• have two membranes: inner and outer membrane
• contains chlorophyll in the grana to trap sunlight energy
• carry out photosynthesis in the chlorophyll
• storage of food and pigments

Organelles – (little organ) tiny structures inside a cell that perform specific functions for a cell. Example: mitochondria, lysosome and chloroplast.

Mitochondria

• Animal: High density at sperm cells (at middle piece to provide sufficient energy for motive power), flight muscle cells (bird / avian), liver cells, meristematic / meristemic cells (involve with cell division), kidney cells, heart muscle cells, brain cells.

Chloroplasts

• Plant: High density at palisade mesophyll (leaf: below upper epidermis). It functions to trap sunlight to synthesise sugar during photosynthesis.

The Uniqueness of The Cell

A cell is unique:

1. Specialisation
2. Division of labour
3. Coordination and integration

Example of specialisation of cells :

• Animal – smooth muscle cell, neuron (nerve cell), white blood cell, red blood cell (erythrocyte), cheek cell (lining epithelial cell), sperm, ovum cell (the biggest cell in human)
• Plant – palisade mesophyll cell, xylem, phloem, guard cell.

Cell Organisation

Unicellular – A single cell performs all the basic life process. Example: Amoeba sp.,Paramecium sp., Chlamydomonas, Bacteria and Euglena.

Multicellular – An organism consists of more than one cell. Each group of cell specialized to carry our life processes. Example: Homo sapien (human), animals and plants. It has five levels of organisation

1. Cells: basic units of structure and function.
   Example: Red blood cells and xylem vessel cells.
2. Tissues: made up of cells with similar in structure and function.
   Example: Epithelial tissues and vascular tissues.
3. Organs: made up of tissues that perform a specific function.
   Example: Heart and flower.
4. System: two of more organs that perform a specific function.
   Example: Digestive system and root system.
5. Organisms: whole living thing that carry out all the basic life processes.
   Example: Human and durian tree.

Cell Organisation (Unicellular) in Amoeba sp. (lives in freshwater ponds) andParamecium sp. (lives in soil and moist area)

1. Cell structure

• Amoeba sp.: plasma membrane, food vacuole, contractile vacuole, pseudopodium, nucleus, ectoplasma, endoplasm.
• Paramecium sp.: food vacuole, posterior contractile vacuole, cytostome, gullet, oral groove, cilia, macronucleus, micronucleus, anterior contractile vacuole.

2. Locomotion

• Amoeba sp.: Pseudopodium (false foot) helps it to move forward slowly and it is known asamoeboid movement.
• Paramecium sp.: Hair-like cilia to beat against water. It beats its cilia backwards diagonally (swim forward) and it rotates on its axis. It beats its cilia forward (swim backwards).

3. Feeding

• Amoeba sp.: Omnivore. Eat bacteria, plant cells, algae and other microscopic organisms.

1. Entrapment – extend pseudopodium.
2. Engulfment – engulf tiny food (phagocytosis) with its pseudopodia.
3. Digestion – food enclosed in food vacuole
4. Absorption – enzyme digests the bacteria
5. Egesting – expel indigestible material.

• Paramecium sp.: Eat bacteria, organic material and other microscopic organisms.

1. Sweeping – movement of cilia. Food moves along the oral groove into the gullet and cytostome.
2. Digestion – food vacuole circulates round the cell.
3. Elimination – undigested food is eliminated at the anal pore.

4. Reproduction

• Amoeba sp.: two types of reproduction.

1. Binary Fission – nucleus divides (favourable condition) and then follows by division of cytoplasm. Two daughter cells are formed (mitotic division).
2. Spore Formation – spores form (bad condition) and germinate into new amoeba under favourable condition.

• Paramecium sp.: two types of reproduction.

1. Binary Fission – micronucleus undergoes mitosis (favourable condition). Macronucleus begins to elongation and form two. Cell content divide and two daughter cells are formed.
2. Conjugation (Sexual reproduction) – two same species parent paramecia exchange genetic material of their micronuclei. Each parent divides and forms four daughter cells.

5. Osmoregulation

• Amoeba sp.: water moves into the cell by osmosis and prevention of bursting, it has a contractile vacuole.
• Paramecium sp.: water moves into the cell by osmosis and prevention of bursting, it has two contractile vacuoles.

6. Respiration

• Amoeba sp. and Paramecium sp. (both): exchange gases throughout the whole cell membrane

7. Excretion

• Amoeba sp. and Paramecium sp. (both): waste products are ammonia and carbon dioxide by diffusion. Solid waste in paramecium is expelled through its anal pore.

Cell Organisation (Multicellular) in Human

1. Cells: Epithelial cells, muscle cells, white blood cells, red blood cells, sperm, nerve cells.
2. Tissues: Epithelial tissue, smooth muscle tissue, connective tissue, skeletal tissue, nerve tissue.
3. Organs: Stomach, heart, kidney, lung, liver.
4. Systems: Circulatory system, respiratory system, digestive system, excretory system, muscular system, lymphatic system, integumentary system, skeletal system, nervous system, endocrine system, reproductive system.
5. Organisms: Human.

Cell Organisation in Plant

1. Cells: Parenchyma cells, collenchyma cells, sclerenchyma cells, epidermal cells.
2. Tissues: Epidermal tissue, meristem tissue, vascular tissue.
3. Organs: Leaf organ, flower organ, stem organ, root organ.
4. Systems: Shoot system, root system.
5. Organisms: Plant.

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