Category: Biology Second Paper

Bipolar neurons have two elongated parts. One is the axon and the other is the dendrite. These later transform into unipolar or multipolar neurons. In the human embryo, there are bipolar neurons in the retina, nose and cochlea.

A unipolar neuron has an elongated segment. It is a sensor. The peripheral nervous system of vertebrates consists of unipolar neurons.

A non-polar neuron has no protracted segment. Apolar neurons are located in the outer layer of the cerebral hemisphere and in the intermediate nuclear layer of the retina.

Neurons can be divided into five categories. namely-
1. Apolar: A non-polar neuron has no protracted segment. Apolar neurons are located in the outer layer of the cerebral hemisphere and in the intermediate nuclear layer of the retina.
2. Unipolar: A unipolar neuron has an elongated segment. It is a sensor. The peripheral nervous system of vertebrates consists of unipolar neurons.
3. Bipolar: Bipolar neurons have two elongated parts. One is the axon and the other is the dendrite. These later transform into unipolar or multipolar neurons. In the human embryo, there are bipolar neurons in the retina, nose and cochlea.
4. Multipolar: Multipolar neurons have many elongated parts. The mammalian brain and spinal cord contain multipolar neurons.
5. Pseudopolar: Pseudopolar neuron has two pronged parts first. Later merge into one. It arises from bipolar neurons. Spinal ganglia and carotic ganglia contain pseudopolar neurons.

The structural, functional and basic unit of nervous system is called neuron. It arises from the neuroplast of the ectoderm. It is accompanied by a special banana called neurogia.

Response to any kind of change inside and outside the organism is called stimulus. In organisms, receptors receive the stimulus, neurons transmit it, and effectors express the response.
The coordination between different cells, organs, organs and systems of the body by the nervous system is called neural coordination. Electrical impulses are transmitted from one cell to another through neurons. Electrical stimulation is then converted into chemical stimulation by neurotransmitters and causes action.

1. Cuticle present on stem.
2. The chondroma is multicellular.
3. The epidermis is composed of collenchyma cells.
4. The cortex can be divided into extracortical and intracortical regions.
5. Pericycles are multilayered.
6. Its vascular bundles are connected, collateral and free.
7. Its metaxylem is towards the periphery and protoxylem towards the center i.e. Endarch.
8. Vascular bundles are located circularly or circularly.
9. Xylem is elongated.
10. Contains marrow and medullary rays.

A thin cross-section of the stem of a dicotyledonous plant shows the following.
1. Epidermis: Epidermis is single layered and composed of parenchyma cells. Cells are densely packed and cysts are absent. It has multicellular chondroma. Cuticles are present outside the skin.
2. Hypodermis: Below the epidermis lies the hypodermis. It is 5-7 layered and composed of collenchyma cells. It has no budget. Some cells contain chloroplasts.
3. Cortex: It is 2/3 layers below the hypodermis. It is composed of parenchyma cells containing chloroplasts. Cells are large and round with intercellular spaces. It stores food.
4. Endodermis: The inner layer of the cortex is called endodermis. It is composed of single-layered and tubular parenchyma cells. The cells are densely packed and without gaps. It is called starch sheath because there are many white grains deposited in the endodermis.
5. Stele: The portion extending from the bottom to the center of the endothelium is known as the styli. Different regions of Stele are-
(i) Pericycle: Pericycle is 3-4 layered and composed of parenchyma or sclerenchyma cells. At the head of the vascular bundle is a cap-like ring made up of sclerenchyma cells. It is called Bundle cap. Pericycle originates from the connective tissue of the head.
ii) Basal tissue: Basal tissue is composed of multi-layered parenchyma cells below the pericycle. The cells are large and the walls are very thin. Vascular bundles are located within this layer.
(iii) Vascular bundles: Vascular bundles are numerous and arranged in two rows in a ring shape. It is connected, parallel and free. Its components are:
Xylem: Metaxylem towards the periphery and protoxylem towards the center i.e. Endarc. Xylem is located between exocambium and endocambium. It transports water. The xylem breaks down to form lysigenous cavities.
Phloem: Phloem is located on both sides of xylem. The phloem outside the xylem is called exophloem and the phloem inside is called endophloem. It transports food.
Cambium: Cambium is located on both sides of xylem. The cambium outside the xylem is called exocambium and the cambium inside is called endocambium. It creates new cells.

1. Cuticle present on stem.
2. Condrom absent.
3. Epidermis is composed of squamous cells.
4. The cortex cannot be divided into extracortex and intracortex.
5. Vascular bundles are connected, contiguous and closed.
6. Its metaxylem is towards the periphery and protoxylem towards the center i.e. endarch.
7. Vascular bundles are scattered.
8. Xylem is Y or V shaped.
9. There is no marrow or medulla.

A thin cross-section of the stem of a monocot plant shows the following.
1. Epidermis: The epidermis is single-layered and composed of parenchyma cells. It lacks chondroma and sacrum. Cuticle present.
2. Hypodermis: Below the epidermis lies the hypodermis. It is multi-layered and composed of squamous cells. It has no budget.
3. Ground tissue: Ground tissue extends from the bottom of the hypoderm to the center. It is multilayered and composed of parenchyma cells. Cells are round and have intercellular spaces.
4. Vascular bundles: Vascular bundles are numerous and scattered. It is connected, adjacent and closed. It does not contain cambium. Vascular bundles are surrounded by a sheath of sclerenchyma cells. It is called bundle sheath. Its components are:
(i) Xylem : Metaxylem towards the periphery and protoxylem towards the center i.e. endarch. Xylem looks like the letter Y or V. The xylem breaks down to form lysigenous cavities.
(ii) Phloem: Phloem is located between the two arms of Y-shaped xylem tissue. It lacks phloem parenchyma.