Cell-Structure and Functions
Introduction to Cells:
With the help of a microscope, an English scientist, Robert Hooke, first discovered the existence of cells in 1665.Scanning electron microscopes are used to examine the external parts of various organisms.The transmission electron microscope is used to view the internal structure of a cell and its organelles.Organisms that are made up of a single cell and perform all their vital activities, like reproduction, locomotion and digestion, are called unicellular organisms.Organisms that are made up of more than one cell are called multicellular organisms.Amoeba uses small finger-like projections called pseudopodia for locomotion and to capture prey.Paramecium is a single cell and is built in such a way that it performs all its vital activities, like reproduction, locomotion, digestion, and so on. The White Blood Corpuscle (WBC) is the only animal cell that changes its shape.The branched structure of a neuron helps it to transfer messages to all parts of the body.
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.Heis known for his book Micrographia, and for first using the word "cell" to describe the basic unit of life.
Scanning electron microscopes are used to examine the external parts of various organisms; It is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample, producing signals that contain information about the sample's surface topography, composition, and other properties such as electrical conductivity.
The transmission electron microscope (TEM) is used to view the internal structure of a cell and its organelles. TEM is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin specimen, interacting with the specimen as it passes through it. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor, such as a CCD camera.
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.
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.
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.
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.
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.
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.
Structure and Function of Cells:
The black layer or the scab that you see on the wound is a result of the aggregation of dead Red Blood Cells (RBCs).The nose and the lungs form part of an organ system, the respiratory system.All organ systems work together to form a complex organism. The cytoplasm is a jelly-like fluid present between the nucleus and the cell membrane.The cell membrane allows the movement of minerals and other substances in and out of the cell.The nucleus controls the activities of a cell.Methylene blue is the stain placed on plant and animal cells to differentiate the nucleus under a microscope.Chromosomes are called vehicles of heredity because they carry genes and help in the inheritance or transfer of characteristics from the parents to the offspring.
Bacteria and blue-green algae that contain nucleoids are called prokaryotes.Organisms that have a well-organised nucleus are called eukaryotes.The nuclear material in unicellular organisms does not contain a nuclear membrane, and hence is called a nucleoid.The nucleolus is a small, spherical body in the nucleus.Chloroplast is a type of plastid involved in photosynthesis in plants.A vacuole is present in both plant and animal cells, but it looks much smaller in animal cells.
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).
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.
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.
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.
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.
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.
Methylene blue is the stain placed on plant and animal cells to differentiate the nucleus under a microscope. Solutions of this substance are blue when in an oxidising environment, but will turn colourless if exposed to a reducing agent.
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.
Bacteria and blue-green algae that contain nucleoids are called prokaryotes.
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.
The nucleoid is an irregularly-shaped region within the cell of prokaryotes, which has nuclear material without a nuclear membrane.
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 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.
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.