Sediments are loose Earth<span> materials such as </span>sand<span> that accumulate on the land surface, in river and </span>lake<span> beds, and on the </span>ocean<span> floor. Sediments form by </span>weathering<span> of rock. They then erode from the site of weathering and are transported by </span>wind<span>, </span>water<span>, </span>ice<span>, and </span>mass wasting<span>, all operating under the influence of gravity. Eventually sediment settles out and accumulates after transport; this process is known as deposition. Sedimentation is a general term for the processes of </span>erosion, transport, and deposition. Sedimentology is the study of sediments and sedimentation.<span>
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Neurotransmitters. With the regard to the process of the neural transmission, a refractory period refers to the time in interval in which. the Positively charged sodium ions are to pumped back to outside a neural membrane.
Neurotransmitters are the chemical messengers that your body can't function without it. Their job is to carry out chemical signals (“messages”) from one of the neuron (nerve cell) to the next target cell. The next target of the cell can be another nerve cell, a muscle cell or the gland.
Fortunately, the seven “small molecule” are neurotransmitters (acetylcholine, dopamine, the gamma-aminobutyric acid (GABA), or glutamate, histamine, norepinephrine, and the serotonin) do the majority of the work.
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The medulla, pons, and the cerebellum are three main parts of the hindbrain.
Brain is the centre of the nervous system. It is enclosed in the skull cranium. The primary regions of the brain are the forebrain, midbrain and the hindbrain. The forebrain consists of the cerebrum and diencephalon. The midbrain is a small tubular region between the forebrain and the hindbrain. The hindbrain is made up of the medulla oblongata, pons and cerebellum.
Cerebellum is the second largest portion of the brain which helps in maintaining the body's equillibrium, coordinates muscular movements and body posture. Pons is the structure located in the brain stem which relays impulses from medulla to cerebellum and vice versa. Medulla oblongata is the lowest part of the brain stem controlling involuntary reflexes and has the respiratory and cardiac centres in it controlling respiration and heart beats respectively.
Tundra and deserts are two biomes of the world which represent the extreme form of climates. Tudra is the coldest region of the earth while desert represent the hottest zones of the earth. But whats the most common thing in these extreme zones is that they receive very less precipitation throughout the year (less than 25 cm).
Therefore, flora of the desert and Tundra have some special adaptations to survive without sufficient amount of water.
Let's see what are those:
- The height of plants growing in Tundra is very less like lesser than 1 foot. The short structure of the plants helps them to get more heat from the dark soil and helps to survive freezing. The short height lets them stay protected from harsh effects of cold or snow.
- The plants in tundra grow in groups or clumps that helps them in surviving the attacks of ice particles or snow balls. For example: lousewort and Arctic crocus.
- Some flora of tundra has ability to grow even in the complete lack of water for several years.This is because they have waxy layers that cover the leaves and store maximum water for the periods of no availability.
- Some plants have hair on the surface of stems that trap maximum heat and protect the plant from heat and extreme forms of wind. For example: Arctic crocus.
- Desert plants not only have physiological but also morphological adaptations to survive heat stress and shortage of water. Their stems, roots and leaves are fleshy and help them to store water for a large period of time. For example: Cactus
- Many desert plants like <em>xerophytic bromeliads</em> and <em>epiphytic orchids </em>contain a system alternate of photosynthesis called CAM (Crassulacean Acid Metabolism). This process helps the plant to open the stomata at night for exchange of gases and accumulate CO2. In day, stomata are closed and the CO2 is used for photosynthesis. This is an adaptation, because during night when temperature is low, CAM plants lose less water as compared to what normal plants lose during day.
- Some plants have extremely large roots that absorb maximum water from soil and compensate the plant's loss of water due to heat. For example: Phreatophytes.
- Some Perennial plants have adapted the mechanism to stay in condition of rest or dormant during extreme heat. They get back to normal life when weather become a bit better.
Hope it helps! :)
Answer:
The second one is correct
Explanation:
A leukocyte is responsible for the immune system
