Answer:
D
Explanation:
Lymphocytes are the second line of defence
First line of defence indiscriminately defends against all pathogens unlike secondary response which is targeted. First line of defence refers to the external body components like skin, secretions from the body in the alimentary canel
Mucus traps pathogens. Stomach acid kills pathogens
Explanation:
Gravitational potential energy is the energy of body due to its position in the gravitational field.
Whereas chemical potential energy is the energy within the chemical bonds of a substance.
For example, when we eat an apple then we get energy in our body so, it is the chemical potential energy stored in the apple.
Items sorted on the bases of gravitational potential energy and chemical potential energy are as follows.
Gravitational potential energy:
- a ball thrown up in the air.
- a stone rolling downhill.
- water stored in an overhead tank.
Chemical potential energy:
- liquid petroleum gasoline used in cars.
- firecrackers that people set off.
There are four main types of tissue: muscle, epithelial, connective and nervous. Each is made of specialized cells that are grouped together according to structure and function. Muscle is found throughout the body and even includes organs such as the heart. Our outer layer of skin is epithelial tissue.
A Nerve electrical impulse only travels in one direction. There are several reasons nerve impulses only travel in one direction. The most important is synaptic transport.
In order for a "nerve impulse" to pass from cell to cell, it must cross synaptic junctions. The nerve cells are lined up head to tail all the way down a nerve track, and are not connected, but have tiny gaps between them and the next cell. These tiny gaps are called synapses.
When you get a nerve firing, you have probably heard that it is an electrical impulse that carries the signal. This is true, but it is not electrical in the same way your wall outlet works. This is electrochemical energy. Neurotransmitters are molecules that fit like a lock and key into a specific receptor. The receptor is located on the next cell in the line. When the neurotransmitter hits the receptor on the next cell in line, it signals that cell to begin a firing as well.
This will continue all the way down the length of the nerve track. In a nutshell, a nerve firing results in a chain reaction down the nerve cell's axon, or stemlike section. Sodium (Na+) ions flow in, potassium (K+) ions flow out, and we get an electrochemical gradient flowing down the length of the cell. You can think of it as a line of gunpowder that someone lit, with the flame traveling down the length of it. Common electrical power is more like a hose full of water, and when you put pressure on one end, the water shoots out the other.
Therefore, nerve impulses cannot travel in the opposite direction, because nerve cells only have neurotransmitter storage vesicles going one way, and receptors in one place.
Robert Hooke is the first person to observe cells as microscopic structures.
He was of British descent and, fun fact, he discovered cells by looking at a sliver of cork under a microscope lens (although the 'fun fact' is heavily simplified).
