Nucleus and Its Functions
Nucleus is the core of the cell and contains the natural material (DNA) as well as controlling all phone activities. In some organisms (prokaryotes) the cell does not have a nucleus. To operate its functions, it has structures known as organelles that useful resource in this. The cell is protected from its surrounding with the aid of the call membrane. All other substances within the cell membrane aside from the nucleus make up cytoplasm. The nucleus itself is surrounded by a pair of membranes called telephone envelop. Within then nucleus, there is chromatin which is a granular material housing the DNA. Also, there are chromosomes that carry the genetic material to be passed to latter generation of cells. Assembly of cell proteins occurs on the ribosome which is made of proteins and RNA material. Carbohydrates, water, proteins and salts are stored in the cell vacuole. Mitochondrion converts food substances stored in the cell into compounds that it requires for its operations (Macauly & Walker, 2008).
How Material Gets into and out of the Cell
The cell membrane allows selective entry of material into and exit from the cell. In plants, some bacteria, and algae it is surrounded by a protective layer known as the cell wall. Movement of material past the cell membrane occurs through either of three processes- diffusion, osmosis, and active transport. The process depends on the relative concentration of the material inside the cell and in its surroundings. The amount of a material (solute) in the solution is known as its concentration. A solution with a higher concentration of the solute is said to be hypertonic and hypotonic if otherwise. Solutions with the equal concentration of the solute are said to be isotonic. When the solution outside the cell is hypertonic, material enter the cell through diffusion. Similarly, material leaves the cell through diffusion if its concentration is higher inside the cell than outside. Water enters or leaves the cell through osmosis by using the selectively permeable cell membrane. Against concentration gradient, material moves into or out of the cell by using energy by a process known as active transport.
Cell Growth and Development
Cell growth happens as either cell development or reproduction (division). The number of cells in an organism multiplies through a process known as doubling. Successive generations of cells have twice the number as previous ones though this is affected by the fact that some cells are lost in the proceedings. The cell exhibits asexual reproduction which allow for the division of the cell and the nucleus into two. The process of division is known as the cell cycle and has four phases. In the G1 phase, there is synthesis of vital enzymes to allow for the replication of DNA material. S phase involves the replication of DNA to produce two identical sets of chromosomes. G2 involves the synthesis of proteins. In the M phase, the nucleus and cytoplasm divide as well as the formation of the cell membrane (Macauly & Walker, 2008).
Classification and Functions of Tissues
Epithelium forms the surface covering on animal body. It mainly helps in protection of internal organs and issues, secretion, adsorption, and sensory reception. Connective tissue supports, protects, and binds together parts of the body. Muscular tissue produces force that causes motion which is vital for locomotion and movement of internal organs. Reception of stimuli and dictation of reaction is done by the neural tissue. In plants, maristematic tissues allow for the increase in length and thickness. Permanent tissues offer protection, support, and synthesis of food.
Macauly, D. & Walker, R. (2008). The way we work: Getting to know the amazing human body, Boston, Houghton Miffin.