Cell is structural, functional and biological unit of all the living organism. They are small unit of life of organisms. The replication process is independent and are known as building block of life. There are two type of cells found in all organisms. Prokaryotic cell that are made up from a single cell and Eukaryotic cell that are made up from two or more than two cells (Lodish et al, 2004). In the later paragraphs the structure and function of both eukaryotic and prokaryotic cells are explained in detail.
Prokaryotic cells are simple cells. They lack cell membrane and organelles. They reproduce by binary fission. They have a cell envelope known as capsule made from polysaccharides. They also have plasma membrane made up of proteins, phospholipids, carbohydrates. Inner to it is cytoplasm, it contains ribosome, mesosomes and plasmids (Whiteman, 1998). The ribosomes exist freely inside the cytoplasm and the mesosomes are folding in the plasma membrane. In Bacteria small Pilli and flagella are present.
Eukaryotic cell are complex. They have membrane bound nucleus. They have a cell wall, inner to it is plasma membrane which is a double layered wall. Inner to it cytoplasm is present which is a jelly like substance in which all other organelles are present. Nucleus is present in the center with a nucleolus inside and covered by nuclear membrane (Raven, 1987). The other organelles that are present include mitochondria, chloroplast, endoplasmic reticulum, ribosome, golgi bodies, lysosomes, vacuoles and all these organelles are present inside the cytoplasm. It also consists of chromosome e present in the nucleolus of the cells.
There are many eukaryotic cells. Among these most important are plant cells and the animal cells.
These are eukaryotic cells which has nucleus that is membrane bound. They are larger in size than to animal cells. They are rectangular or cuboidal in shape. The cell wall is present outside the plasma membrane and is made of cellulose and functions to support and provide rigidity. They have membrane bound cell structures (Albert et al, 2002). The organelles carry out functions like producing hormone, enzyme and carrying out metabolic activities.
The animals are multicellular so eukaryotic cells. They are covered by cell membrane but do not have a cell wall. The animal cells consists of are centrioles, cilia and flagella, endoplasmic reticulum, Golgi apparatus, lysosomes, microfilaments, microtubules, mitochondria, nucleus, peroxisomes, plasma membrane and ribosomes (Margulis, 2000).
Cell wall: The outermost covering meant for support, rigidity and protection.
Cell membrane: Inner to cell wall made up of phospholipid
Cytoplasm: All the organelles reside in this
Nucleus: inside the cytoplasm and contains hereditary information of the cell that is inside the DNA.
Chloroplast: Plastid containing chlorophyll meant for trapping light energy and carrying out photosynthesis.
Mitochondria: Power house of the cell. They are present inside the cytoplasm.
Vacuoles: Temporary storage unit of cell
Golgi complex: Proteins are sorted and packed in it.
Ribosomes: Meant for assembling proteins
Endoplasmic reticulum: Meant for transporting material
The cell membrane present is a semi permeable membrane. It is double layered made up of phospholipids with proteins embedded inside it. The major function of cell membrane are as follows:
Isolating the cytoplasm from the outside environment
Regulating the exchange of substances in to and out of the cell
Communicating with other cells
The substance move across the membrane in a passive that is coming in absence of input of cell’s energy or active which expands the cell energy and than transport it. It also make up the cell potential. Thus making the cell membrane a filter and allowing a specific amount of things to go out and come inside the cell. Phospholipids are made up of a hydrophilic head and a tail that is hydrophobic and forms a barrier. The small particle which does not have charge easily passess through the membrane bilayer like carbon dioxide and oxygen. The water molecules are charged so does not pass easily, and requires a channel protein known as Aquaporin to pass through the membrane (Jesse et al, 2007). The transport mechanism is passive which takes place by simple diffusion, facilitated diffusion by help of proteins, osmosis and with the help of contractile vacuoles or central vacuoles. The transport mechanism which is active involving the movement of molecule uphill that is going against the concentration gradient is carried up with the help of ATP molecules. It involves three processes of endocytosis, exocytosis or by the aid of sodium and potassium pump.
Explain the terms active and passive transport of substances across a membrane?
Active transport is the movement of biomolecules from the region of low concentration to the region of high concentration with the help of chemical energy (Nelson, 2005). The types of active transport are Endocytosis, exocytosis and sodium-potassium pump.
The Passive transport is movement of biomolecules from the region of high concentration to the region of low concentration and without the help of any kind of chemical energy. The type of passive transport are diffusion, facilitated diffusion and osmosis.
Name a substance that moves by each mechanism
The proteins and ions move via the active transport process (Wächtershäuser, 2003).
The water and oxygen molecules move up by the passive process.
Explain why the process of mitosis is important in cells
Mitosis is necessary because by it the division of parent genome takes place and it is divided in to two same copies of the two daughter genome. In both the animal and plant cell mitosis helps the tissues to grow, body parts to grow and repair any abnormalities.
Describe the key stages in the process of mitosis
Mitosis is the division of cell in to two identical daughter cells. It consists of four stages:
Prophase: Duplication of DNA takes place and cell is prepared for dividing. The nuclear membrane disrupts in this phase (Morgan & David, 2007).
Metaphase: The chromosomes along with their chromatids are aligned aloe equator or the metaphasic plate. The spindle fibre formation begins.
Anaphase: The two sister chromatids separate and try to move to the end of the poles of spindle
Telophase: The cell membrane closes up and split the cell in to two half’s. It gives two daughter cells with same genome.
Name the process in animals which require meiosis to take place
Reproductive cells known as germ cells requires meiosis to take place.
Outline the stages of meiosis describing the key chromosome movements which occur
The stages of meiosis in which the chromosome movement occurs during the prophase I of meiosis I. These are:
Explain the biological importance of meiosis?
The biological importance of meiosis is that by this the haploid gametes are formed which carry out sexual reproduction(Freeman, 2002). It also results in maternal and paternal genes being exchanged during crossing over and allowing variations to occur in the offspring’s. It also maintains the same chromosome number that is n in all the daughter chromosomes.
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