Biology Write short notes

a. Nucleus contains the genetic material of an organism.
b. This genetic material is present in the form of Deoxyribonucleic Acid (DNA) which is responsible for synthesis of various proteins and enzymes.
c. These proteins and enzymes in turn regulate metabolic activities of the cells.
Therefore, nucleus is considered as control unit of a cell.

Lysosomes:

1. Lysosomes are considered as dismantling and restructuring units of a cell.
2. These are membrane bound vesicles containing hydrolytic enzymes. The enzymes in lysosomes are used by most eukaryotic cells to digest (hydrolyse) macromolecules.
3. The lysosomal enzymes show optimal activity in acidic pH.
4. Lysosomes arise from Golgi associated endoplasmic reticulum.
5. Lysosomes are polymorphic in nature and are classified as primary lysosomes, secondary or hybrid lysosomes, residual body and autophagic vesicle.
6. The list of lysosomal enzymes includes:
   All types of hydrolases viz, amylases, proteases and lipases.

Cell is defined as a structural and functional unit of life of all living organisms capable of independent existence and can perform all functions of life.

Ribosomes are the protein factories that synthesize proteins using genetic information.

Chloroplast plays a significant role in synthesis of starch in plants.
Structure of chloroplast:

1. In plants, chloroplast is found mainly in mesophyll of leaf.
2. Chloroplast is lens shaped but it can also be oval, spherical, discoid or ribbon like.
3. A cell may contain single large chloroplast as in Chlamydomonas or there can be 20 to 40 chloroplasts per cell as seen in mesophyll cells.
4. Chloroplasts contain green pigment called chlorophyll along with other enzymes that help in production of sugar by photosynthesis.
5. Inner membrane of double membraned chloroplast is comparatively less permeable.
6. Inside the cavity of inner membrane, there is another set of membranous sacs called thylakoids.
7. Thylakoids are arranged in the form of stacks called grana (singular: granum).
8. The grana are connected to each other by means of membranous tubules called stroma lamellae.
9. Space outside thylakoids is filled with stroma.
10. The stroma and the space inside thylakoids contain various enzymes essential for photosynthesis.
11. Stroma of chloroplast contains DNA and ribosomes (70S).

Plastids are double membraned organelles containing DNA, RNA and 70S ribosomes.

The organelle which helps in maintaining turgidity of the cell and a proper internal balance of cellular contents is known as vacuole.

1. The vacuoles are bound by semipermeable membrane, called tonoplast membrane. This membrane helps in maintaining the composition of vacuolar fluid (cell sap), different from that of the cytosol.
2. Composition of cell sap differs in different types of cells.
3. In vacuoles along with excretory products other compounds are stored that are harmful or unpalatable to herbivores, thereby protecting the plants.
4. Attractive colours of the petals are due to storage of such pigments in vacuoles.
5. Generally, there are two or three permanent vacuoles in a plant cell.
6. In some large plant cells, a single large vacuole occupies the central part of the cell. It is called central vacuole. In such cells, vacuole can occupy about 90% of the total volume of the cell.
7. The cell sap of central vacuole is a store house of various ions and thus is hypertonic to cytosol.
8. Small vacuoles in seeds of certain plants store organic materials like proteins.
9. In animal cells, they are few in number and smaller in size.
10. Intake of food or foreign particle by phagocytosis involves formation of food vacuole.

Lysosomes:

1. Lysosomes are considered as dismantling and restructuring units of a cell.
2. These are membrane bound vesicles containing hydrolytic enzymes. The enzymes in lysosomes are used by most eukaryotic cells to digest (hydrolyse) macromolecules.
3. The lysosomal enzymes show optimal activity in acidic pH.
4. Lysosomes arise from Golgi associated endoplasmic reticulum.
5. Lysosomes are polymorphic in nature and are classified as primary lysosomes, secondary or hybrid lysosomes, residual body and autophagic vesicle.
6. The list of lysosomal enzymes includes:
   All types of hydrolases viz, amylases, proteases and lipases.

Cytoplasm in Eukaryotic cell:

1. The cell contains ground substance called cytoplasmic matrix or cytosol.
2. This colloidal jelly like material shows streaming movements called cyclosis.
3. The cytoplasm contains water as major component along with organic and inorganic molecules like sugars, amino acids, vitamins, enzymes, nucleotides, minerals and waste products.
4. It also contains various membrane-bound cell organelles like endoplasmic reticulum, Golgi complex, mitochondria, plastids, nucleus, microbodies and cytoskeletal elements like microtubules.
5. Cytoplasm acts as a source of raw materials as well as seat for various metabolic activities taking place in the cell.
6. It helps in distribution and exchange of materials between various cell organelles.

In plants, cell wall shows middle lamella, primary wall and secondary wall
1. Middle lamella:
It is thin and present between two adjacent r cells. It is the first structure formed from cell plate during cytokinesis. It is mainly made up of pectin, calcium and magnesium pectate. Softening of ripe fruit is due to solubilization of pectin.
2. Primary wall:
In young plant cell, it is capable of growth. It is laid inside to middle lamella.
It is the only wall seen in meristematic tissue, mesophyll, pith, etc.
3. Secondary wall:
It is present inner to primary wall. Once the growth of primary wall stops, secondary wall is laid. At some places thickening is absent which leads to formation of pits.