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About Cell


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Cell Structure and Functions:

Cell Structure and Functions SHUVAM MAHAPATRA Std - VIII, Section-C Admiission 1578 2013-2014

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A  microscope  is an instrument used to see objects too small for the naked eye. An English scientist,  Robert Hooke , discovered the existence of cells in 1665. He used the word “cell” to describe the basic unit of life Discovery of Cells Robert Hooke Observed sliver of cork Saw “row of empty boxes” Coined the term cell


Cells Smallest living unit Most are microscopic

Principles of Cell Theory:

Principles of Cell Theory All living things are made of cells Smallest living unit of structure and function of all organisms is the cell All cells arise from preexisting cells

Cell Size:

Cell Size

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Organisms that are made up of a single cell and perform all their vital activities, like reproduction, locomotion and digestion, are called  unicellular  organisms. Unicellular organisms can be found everywhere. The oldest forms of life, unicellular organisms existed 3.8 billion years ago, if not longer.

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Organisms that are made up of more than one cell are called  multi-cellular  organisms. Most life that can be seen with the naked eye are multi-cellular, as are all animals and plants.

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Amoeba  uses small finger-like projections, called  pseudopodia,  for locomotion and to capture prey. Pseudopods or pseudopodia are temporary projections of eukaryotic cells. Cells with these structures are called ameboids .

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Paramecium  is a single cell, and is built in such a way that can perform all vital activities, like reproduction, locomotion, digestion, and so on.

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The  White Blood Corpuscle  (WBC) is the only animal cell that changes its shape. WBC’s are responsible for protecting our bodies against invading bacteria and harmful micro-organisms. To find invading bacteria, they travel along with blood in blood vessels. Whenever they find invading bacteria, they squeeze through the blood vessels and intercellular spaces, catch the bacteria and kill it. To perform this task, WBC’s change their shape using pseudopodia similar to those in an amoeba.

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The branched structure of a  neuron  helps it transfer messages to all parts of the body. A neuron, also known as a nerve cell, is an electrically excitable cell that processes and transmits information by electrical and chemical signalling.

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The black layer or  scab  (a hard coating on the skin formed during the wound healing reconstruction phase) that you see on a wound is a result of the aggregation of dead  Red Blood Cells (RBC’s) .

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The human respiratory system consists of the nostrils, nasal passage, internal nares, pharynx, larynx, trachea, bronchi, bronchioles and alveoli. Alveoli are the functional units of the lungs.

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All organ systems work together to form a complex organism. Organ systems include the digestive system, respiratory system, circulatory system, excretory system and nervous system.

Organisms and Cells:

Organisms and Cells d. c. b. a. 50 m 140 m

Representative Animal Cell:

Representative Animal Cell

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Cytoplasm  is a thick liquid in a cell that holds the organelles, except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm. Within the cells of eukaryotes organisms, the contents of the nucleus are separated from the cytoplasm. Cytoplasm

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The  cell membrane  is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It consists of the phospholipid bilayer with embedded proteins. Cell membranes are involved in a variety of cellular processes, such as cell adhesion, ion conductivity and cell signalling, and serve as the attachment surface for extracellular material and intercellular cytoskeleton.   Cell Membrane

Representative Plant Cell:

Representative Plant Cell

Plant Cell:

Plant Cell The  nucleus  controls the activities of a cell. The  nucleus  is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organised as multiple long linear DNA molecules to form chromosomes. The genes within these chromosomes are the cell's nuclear genome. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression. The nucleus is, therefore, the control centre of the cell.

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Chromosomes are called the vehicles of heredity because they carry genes, and help in the  inheritance  or transfer of characteristics from the parents to the offspring. A  chromosome  is an organised structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. Chromosomes


Prokaryotes Bacteria and blue-green algae that contain nucleoids are called  prokaryotes .


E ukaryotes Organisms that have a well-organised nucleus are called eukaryotes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Greek  eu , meaning "good", and karyon , meaning "nut" or "kernel". Most eukaryotic cells also contain other membrane-bound organelles.


Nucleoid The  nucleoid  is an irregularly-shaped region within the cell of prokaryotes, which has nuclear material without a nuclear membrane.


Nucleolus The  nucleolus  is a small, spherical body in the nucleus. It is a non-membrane bound structure composed of proteins and nucleic acids. Ribosomal RNA is transcribed and assembled within the nucleolus.

Chloroplast :

Chloroplast  Chloroplast  is a type of  plastid  involved in photosynthesis in plants. These are specialised organelles found in all higher plant cells. These organelles contain the plant cell's  chlorophyll , providing the green colour. They have a double outer membrane. Within the stroma are other membrane structures, the  thylakoids  and  grana  where photosynthesis takes place.


V acuole A  vacuole  is a membrane-bound organelle present in all plant, fungal cells, and some animal and bacterial cells. Vacuoles are essentially enclosed compartments filled with water containing inorganic and organic molecules, including enzymes, in solution. In certain cases, though, vacuoles may contain solids that have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles, and are effectively just larger forms of these. The organelle has no basic shape or size, and its structure varies according to the needs of the cell.

Golgi Apparatus:

Golgi Apparatus Involved in synthesis of plant cell wall Packaging & shipping station of cell 1. Molecules come in vesicles 2. Vesicles fuse with Golgi membrane 3. Molecules may be modified by Golgi 4 . Molecules pinched-off in separate vesicle 5. Vesicle leaves Golgi apparatus 6. Vesicles may combine with plasma membrane to secrete contents Functions


Lysosomes Contain digestive enzymes Functions Aid in cell renewal Break down old cell parts Digests invaders

Bacteria-Like Organelles:

Bacteria-Like Organelles Release & store energy Types Mitochondria (release energy) Chloroplasts (store energy)


Mitochondria Have their own DNA Bound by double membrane Break down fuel molecules ( cellular respiration) Glucose Fatty acids Release energy ATP


Chloroplasts Derived form photosynthetic bacteria Solar energy capturing organelle

Chloroplast Structure:

Chloroplast Structure double membrane outer membrane inner membrane grana thylakoid space thylakoid membrane stroma a. b. 500 nm


Photosynthesis Takes place in the chloroplast Makes cellular food – glucose

Cell Types:

Cell Types Prokaryotic Eukaryotic

Prokaryotic Cells:

Prokaryotic Cells First cell type on earth Cell type of Bacteria and Archaea No membrane bound nucleus Nucleoid = region of DNA concentration Organelles not bound by membranes

Eukaryotic Cells:

Eukaryotic Cells Nucleus bound by membrane Include fungi, protists , plant, and animal cells Possess many organelles

Thank You:

Thank You

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