CELLS: The Building Blocks of Life

1. CELLS: The Building Blocks of Life

2. History of the Cell • Robert Hooke is a scientist from England. • He experimented with clocks, telescopes and microscopes. • He became famous for the observation of thin slices of bark through the microscope in 1667. • It was this observation that led him to….THE DISCOVERY OF THE CELL !

3. How did he discover the Cell? • He sharpened his knife as keen as a razor blade. • He cut off a very thin piece of cork with his knife. • He placed the thin piece of cork on a black object plate. • Through the microscope, he observed that the cork cells were perforated and porous, much like a honeycomb.

4. CORK CELLS

5. Microscopes

6. Micrographs What is it? A camera can be fitted to a microscope to take pictures. This picture is called the micrograph.

7. Micrographs

8. What does a cell consist of?

9. What does a cell consist of? cell wall cytoplasm nucleus

10. What does a cell consist of ? Protoplasm • Nucleus + Cell surface membrane + Cytoplasm Organelles - Specialised structures within the cell

11. Parts of a Cell The protoplasm of a cell is made up of three parts: • Cytoplasm • Protoplasm between the cell surface membrane and nucleus • Where most cell activities occur • Contains enzymes and specialised structures (organelles) • Cell surface membrane • Surrounds the cytoplasm • Partially permeable • Hence controls substances entering or leaving the cell nucleoplasm nucleolus chromatin nuclear envelope • Nucleus • Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin • Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

12. Cell surface membrane (plasma membrane) Cell surface membrane Animal cell Plant cell

13. Cell surface membrane (plasma membrane) Photomicrograph Cell surface membrane Onion epithelial cell Cheek cell

14. Cell wall • Non-living cell wall made of cellulose that encloses the entire plant cell, surrounding the cell membrane. • The cell wall is fully permeable and is absent in animal cells. Function: • It protects the cell from injury and gives the plant cell a fixed shape.

15. What does a cell consist of? Cell wall • Only exist in plant cells • Absent in animal cells

16. What does a cell consist of? Photomicrograph Cell wall

17. Parts of a Cell The protoplasm of a cell is made up of three parts: • Cytoplasm • Protoplasm between the cell surface membrane and nucleus • Where most cell activities occur • Contains enzymes and specialised structures (organelles) • Cell surface membrane • Surrounds the cytoplasm • Partially permeable • Hence controls substances entering or leaving the cell nucleoplasm nucleolus chromatin nuclear envelope • Nucleus • Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin • Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

18. Cytoplasm Cytoplasm

19. Cytoplasm Cytoplasm Drawing of Onion epithelial cell Cheek cell

20. Parts of a Cell The protoplasm of a cell is made up of three parts: • Cytoplasm • Protoplasm between the cell surface membrane and nucleus • Where most cell activities occur • Contains enzymes and specialised structures (organelles) • Cell surface membrane • Surrounds the cytoplasm • Partially permeable • Hence controls substances entering or leaving the cell nucleoplasm nucleolus chromatin nuclear envelope • Nucleus • Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin • Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

21. Nucleus

22. Nucleus- what is inside? Chromatin • -A network of thread-like structures in the nucleus • -It controls the activities of the cell, such as cell division • -Each chromatin is made up of proteins and deoxyribonucleic acid (DNA) • DNA contains: • -Hereditary information • -Instructions that a cell needs for carrying out all chemical reactions within itself.

23. Nucleus- what is inside? • Chromosome - When the cell is dividing, chromatin condenses and becomes highly coiled structures called chromosomes (which appear as thick, rod-shaped structures under light microscope) chromosome

24. The Nucleus Nucleus

25. The nucleus Nucleus Onion epithelial cell Cheek cell

26. Vacuole • -Fluid-filled space enclosed by a membrane • -Contained in the cytoplasm • Function: -Storage of substances within the cell

27. Vacuole

28. Vacuole Vacuole

29. Vacuole

30. Chloroplast • -Oval structures found in plant cells • -Found in the cytoplasm • Function: • -Contains the green pigment chlorophyll, which is essential for plants to make food (the process of photosynthesis)

31. The chloroplast Chloroplast • Only exist in plant cells • Absent in animal cells

32. Chloroplast Photomicrograph Chloroplasts

33. Chloroplast Electronmicrograph

34. Mitochondria (sin: Mitochondrion) • -Small, sausage-shaped • -Can be seen clearly under electron microscope • Function: • - Aerobic respiration occurs in the mitochondria • -Aerobic respiration is the process whereby food substances are oxidised to give energy the cell needs to carry out activities like growth and reproduction

35. Mitochondria Electronmicrograph of mitochondrion

36. Mitochondria Electron- micrograph:

37. Mitochondria Electron- micrograph: (b) A plant cell

38. Mitochondria Electronmicrograph:

39. Ribosome • Small, round structures • Either attached to certain membranes in the cells or lie freely in the cytoplasm. • Function: • Synthesize proteins in the cell

40. Ribosomes Electron- micrograph:

41. In summary- Most cells share certain features: Protoplasm Cytoplasm Nucleus • Gel-like substance • forming major part of cell • Site where most • organelles are found: • Mitochondria (sausage • shaped) • -for cell respiration • Centrioles - • involved in cell division • Chloroplasts - • Contains chlorophyll, • green pigment needed for • photosynthesis • Vacuoles - • fluid-filled storage sacs • Ribosomes- • Synthesise proteins Cell surface membrane Nucleoli- Building proteins Nucleoplasm- small round mass of protoplasm called the nucleoplasm Nuclear envelope- Separates nuclear content from the surrounding Cytoplasm Chromatin threads- Found in nucleoplasm, contain hereditary materials which condense to form chromosomes • Partially permeable • membrane covering • of cell • Controls substances • entering and leaving cell

42. Cell seen under electron microscope

44. Rough endoplasmic reticulum • Rough endoplasmic reticulum (RER) has a surface that appears rough because of small particles called ribosomes that are attached to its outer surface. The outer surface of the RER is continuous with the nuclear envelope. • Ribosomes are small round structures that are either attached to the membrane of the RER or lie freely in the cytoplasm. They are needed to synthesise proteins. • The ribosomes attached to the RER make proteins that are usually transported out of the cell • The ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of that cell. • The RER transports proteins made to the Golgi apparatus for secretion out of the cell.

45. Smooth endoplasmic reticulum • The smooth ER (SER) does not have ribosomes attached to its membrane. SER is more tubular that than the RER. It is connected to the RER. • The SER synthesises fats and steroids and converts harmful substances into harmless materials.

46. Golgi apparatus • Golgi apparatus or Golgi body is shaped like a disc. • It consists of a stack of flattened spaces surrounded by membranes. Vesicles or tiny spherical spaces enclosed by a membrane can be seen fusing with one side of the Golgi apparatus and pinching off from the opposite side. • The Golgi apparatus stores and modifies substances made by the ER and packages these substances in vesicles for secretion out of the cell.

47. Plant and animal cells: Similarities • Both have nuclei • Both have cell membranes • Both have cytoplasm • Both have mitochondria, ribosomes, ER, Golgi apparatus, vesicles

48. Plant and animal cells: Differences Many small vacuoles A large central vacuole Chloroplasts present No chloroplasts No cell wall Cellulose cell wall centrioles present No centrioles No regular shape Regular shape

49. Differentiation • Growth in an organism involves cell division. • New cells produced may change and develop into new tissues. • This process by which a cell becomes specialised for a specific function is called differentiation. Cells may develop special structures or lose certain structures for them to carry out specific functions. e.g. Human cells become differentiated to form various types of cells: liver cells, muscle cells, sperm cells, epithelial cells, blood cells, etc e.g. Plant cells differentiate to form xylem cells, phloem cells, etc

50. Root Hair Cell Long and narrow to increase the surface area: volume ratio, thus water and mineral salts can be efficiently absorbed from the soil. Absorption of water & mineral salts from soil