Cells are the basic structural and functional units of all living organisms. There are two main types of cells - prokaryotic and eukaryotic. Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells have a nucleus enclosed in a membrane and membrane-bound organelles. The human body contains many different types of cells including nerve cells, sperm cells, white blood cells, and muscle cells. All cells contain three main parts - the plasma membrane, nucleus, and cytoplasm. Within the cytoplasm are various cell organelles that perform specialized functions necessary for cell survival and processes.

1. BY-
Avinash Nayak
Class- IX-C,Kendriya Vidyalaya,
Fort William
Roll No- 1 , Year- 2003

2. Cell is the structural and functional unit of all life forms. All cells, whether they exist as one celled organisms or as part of a multi cellular organism, perform certain basic functions which are essential for their survival. Cells vary in shape, size, function and numbers.

3. Prokaryotic cells are incomplete and undeveloped cells which lack nuclear membrane and contain a single chromosome.
Eukaryotic cells are complete and developed cells which have membrane-bound cell organelles and have many chromosomes.

4. SOME TYPES OF CELLS IN
HUMAN BODY
Nerve Cell
Sperm
White Blood Cell
Muscle Cells
Red Blood Cell

5. DIFFERENT TYPES OF CELLS IN HUMAN BODY
NEURONS
CELLS LINING
INTESTNAL TRACT
BONE CELL
FAT CELL

6. PARAMAECIM
EUGLENA
AMOEBA

7. The largest cell is Ostrich egg.
The smallest cell is Bacteria.
The smallest cell in human body is Red Blood Cell and the largest cell in human body is Nerve cell.

8. TYPES OF CELLS-
(a) Animal Cell
(b) Plant Cell

11. All cells have three major functional regions- Plasma membrane, Nucleus and Cytoplasm. They are the most important parts of the cell.
Plasma Membrane
Cytoplasm
Nucleus

12. Plasma membrane is the outer covering of each cell, which seperates its contents from the surrounding medium. It is made up of lipids and proteins and provides a mechanical barrier for the protection of the inner cell contents. The main function of the cell membrane is to regulate the movement of molecules in and out of the cell. The plant cells, in addition, have a rigid cell wall that lies outside the plasma membrane. Cellulose, the main component of cell wall, is responsible for providing structural strength to plants.

13. Nucleus, the most important part of a cell, is usually located at the centre of the cell. It is controlling part of all cell activities. It is enclosed by a double layered membrane call nuclear membrane. The chief components of nucleus are – Chromatin material and Nucleus. Chromatin material which is in the form of thread like structures consists of DNA ( Deoxyribonucleic acid ) is responsible for storing and transmitting the hereditary information from one generation to another. Nucleolus contains RNA (Ribonucleic acid ) which is helpful in protein synthesis in cytoplasm.

15. Cytoplasm is the jelly-like remaining part of the cell other than nucleus. It contains various cell organelles. These organelles perform the different important functions of a cell.

17. A cell has to perform several functions such as synthesize substances, secrete, digest, generate energy, etc. These activities of the cell are performed by different cell organelles. These cell organelles are enclosed by membranes.

18. It is a membrane network, enclosing a fluid-filled lumen. It is of two types- Rough endoplasmic reticulam with ribosome attached to its surface for synthesizing proteins and smooth endoplasmic reticulam for secreting lipids. Some proteins and lipids synthesized in endoplasmic reticulam are used for producing new cellular parts. Some other function as enzymes and hormones inside the cell or when secreted out of the cell.
Rough Endoplasmic Reticulam

20. The golgi apparatus consists of a set of smooth, flattened cisternae. These are usually stacked together in parallel rows. Golgi apparatus is the secretory organelle of the cell. It packages material synthesized in the Endoplasmic reticulam and despatches it to intracellular and extracellular targets. Golgi apparatus is also involved in the formation of lysosomes and perixosomes. Golgi apparatus is called Dictosomes when present in plants.
Golgi Apparatus

22. Peroxisomes are small membrane- bound sacs and contain powerful oxidative enzymes. They are mostly found in kidney and liver cells. These are specialized for carrying out some oxidative reactions, which include removal of toxic substances.
Peroxisomes

23. Lysosomes are the membrane bound vesicles. They contain powerful enzymes capable of digesting or breaking down all organic material. These serve as intracellular digestive system, hence called “digestive bags”. They destroy any foreign material.They also remove the worn-out and poorly working cell organelles by digesting them to make way for their new replacement.

24. Mitochondria are rod-shaped organelles. Each one is bordered by a double membrane. The outer membrane is smooth and the inner one folded into finger-like cristae, which greatly increase the surface area of the membrane. Mitochondria contain enzymes for cellular respiration in which energy is released. Hence they are also called “power plants” of the cell. Energy in the food molecules is converted here into usable energy and stored as ATP molecules.
Mitochondria

26. Plastids are found in plant cells only. They have double membranes. They can be grouped into two classes with a variety of functions. The colourless Leucoplasts are for forming and storing of starch grains and oil drops. The pigmented Chromoplasts with different colors of several types. The most important ones are the chloroplasts, which contain the pigment chlorophyll which is responsible for food preparation by photosynthesis. Other chloroplasts contain non-green pigments and are responsible for characteristic colours of fruits and flowers.
Chloroplasts

28. Centrosome consists of two granule like centrioles and is found in animal cells only. Centrosome helps in cell division. In plant cells, polar caps perform the same function.
Centrosome

29. In animal cells, Vacuoles are small and many. In plants a single prominent vacuole occupies about 90% of the volume of the cell. Vacuoles are full of liquid cell sap and thus provide turgidity and rigidity to plant cells.
Vacuole In A Plant Cell

30. Cell multiplication or cell division is needed for the growth , development and repair of the body. Cell multiplies by dividing itself again and again. There are two types of cell division – Mitosis And Meiosis.

31. Mitosis cell division occurs in all somatic cells. In this type of cell division, chromosome number remains same, hence it is called equational division. Two daughter cells are produced and no crossing over takes place. One cell division involves four phases- Prophase, Metaphase, Anaphase and Telophase. In mitosis, daughter cells have identical chromosomes to parent cells and genetic material remains constant.

32. Meiosis cell division occurs only in reproductive cells. In this type of cell division, chromosome number reduces to half, hence it is called reductional division. Four daughter cells are produced and crossing over takes place. Meiosis consists of two subdivisions- Meiosis I and Meiosis II each involving four phases. In meiosis, daughter cell chromosomes with combined components of both parents and genetic variability occurs.

33. Same as mitosis.
Two daughter cells are produced
and no crossing over takes place.
One cell division involves four phases-
Prophase, Metaphase, Anaphase and Telophase.

34. Meiosis II is similar to mitosis. However, there is no "S" phase. The chromatids of each chromosome are no longer identical because of recombination. Meiosis II separates the chromatids producing two daughter cells each with 23 chromosomes (haploid), and each chromosome has only one chromatid.

36. I want to thank Mrs. M. Chopra,our science teacher and my mother for their help and I also want to thank the following resources because of whom I have succeeded in completing my Science Project Work.
(a)Microsoft Encarta
(b)Science Textbook- Class IX
(c)Site- www.yahoo.com
(d)Site- www.google.com
(e)“New Course” Science Refresher