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CELLS: The Building Blocks of Life. 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.
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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 !
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.
Micrographs What is it? A camera can be fitted to a microscope to take pictures. This picture is called the micrograph.
What does a cell consist of? cell wall cytoplasm nucleus
What does a cell consist of ? Protoplasm • Nucleus + Cell surface membrane + Cytoplasm Organelles - Specialised structures within the cell
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.
Cell surface membrane (plasma membrane) Cell surface membrane Animal cell Plant cell
Cell surface membrane (plasma membrane) Photomicrograph Cell surface membrane Onion epithelial cell Cheek cell
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.
What does a cell consist of? Cell wall • Only exist in plant cells • Absent in animal cells
What does a cell consist of? Photomicrograph Cell wall
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.
Cytoplasm Cytoplasm
Cytoplasm Cytoplasm Drawing of Onion epithelial cell Cheek cell
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.
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.
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
The Nucleus Nucleus
The nucleus Nucleus Onion epithelial cell Cheek cell
Vacuole • -Fluid-filled space enclosed by a membrane • -Contained in the cytoplasm • Function: -Storage of substances within the cell
Vacuole Vacuole
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)
The chloroplast Chloroplast • Only exist in plant cells • Absent in animal cells
Chloroplast Photomicrograph Chloroplasts
Chloroplast Electronmicrograph
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
Mitochondria Electronmicrograph of mitochondrion
Mitochondria Electron- micrograph:
Mitochondria Electron- micrograph: (b) A plant cell
Mitochondria Electronmicrograph:
Ribosome • Small, round structures • Either attached to certain membranes in the cells or lie freely in the cytoplasm. • Function: • Synthesize proteins in the cell
Ribosomes Electron- micrograph:
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
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.
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.
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.
Plant and animal cells: Similarities • Both have nuclei • Both have cell membranes • Both have cytoplasm • Both have mitochondria, ribosomes, ER, Golgi apparatus, vesicles
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
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
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