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Yogita Ingle 6 years, 10 months ago
The theory behind Mass flow hypothesis which is also called as pressure flow hypothesis describes the movement of sap via phloem, proposed by the German physiologist Ernst Munch in 1930. A highly concentrated organic sugar especially sugar in the cells of phloem from a source like a leaf forms a diffusion gradient which draws water in the cells from adjacent xylem. This develops turgor pressure in the phloem which is also called as hydrostatic pressure.
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Meghna Thapar 5 years, 4 months ago
There are three primary meristems: the protoderm, which will become the epidermis; the ground meristem, which will form the ground tissues comprising parenchyma, collenchyma, and sclerenchyma cells; and the procambium, which will become the vascular tissues (xylem and phloem). There are three types of meristematic tissues: apical (at the tips), intercalary (in the middle), and lateral (at the sides). At the meristem summit, there is a small group of slowly dividing cells, which is commonly called the central zone.
Posted by R G 6 years, 10 months ago
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Yogita Ingle 6 years, 10 months ago
Meristematic tissue or meristems, as they are also called are tissues that have the ability to enlarge, stretch and differentiate into other types of cells as they mature. The cells of this tissue are generally young and immature, with the power of continuous division.
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Meghna Thapar 5 years, 4 months ago
The characters which distinguish the classes.
<th>| Flower parts in multiples of three | Flower parts in multiples of four or five |
| Major leaf veins parallel | Major leaf veins reticulated |
| Stem vacular bundles scattered | Stem vascular bundles in a ring |
| Roots are adventitious | Roots develop from radicle |
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Meghna Thapar 5 years, 4 months ago
An algal bloom is an accumulation of algae (typically microscopic) or a rapid increase in their amount in a body of water. Algal blooms may occur in fresh water as well as salt water. Algal bloom concentrations may reach millions of cells per milliliter of water. Algal blooms are often green, but they can also be other colors such as yellow-brown or red, depending on the species of algae. So-called algal blooms are often caused by Cyanobacteria such as Aphanizomenon flosaquae, which are no longer considered to be algae. Some kinds of algal blooms, such as red tides, are poisonous.
Algal blooms are often caused by eutrophication. Eutrophication occurs when abnormal amount of nutrients, especially phosphorous and nitrogen, enter a body of water. Algal blooms are a big problem to ecosystems because, like any sudden unnatural growth, it harms the other animals in that ecosystem, usually decreasing their numbers quickly.
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Meghna Thapar 5 years, 4 months ago
The pisces include the fishes which have paired appendages known as pectoral and pelvic fins. They respire by gills and have dermal scales which form the exoskeleton. The tetrapoda include the amphibian, mammalian, reptilian and aves which have paired appendages as a five digit limb. They respire by lungs and have epidermal scales, feathers and hairs which form the exoskeleton. The heart of fishes is 2 chambered. They have internal ear but do not have the internal nares. The heart of tetrapoda can be 3 or 4 chambered. They have middle, internal and external ear and also have the internal nares. Fishes are aquatic but tetrapoda can be aquatic or land living.
Posted by Kriti Sharma 6 years, 10 months ago
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Meghna Thapar 5 years, 4 months ago
The axon or nerve fibres are in the form of a cylinder wherein the interior of the axon is filled with axoplasm and the exterior is covered with axolemma. The nerve fibres are immersed in ECF. The solution is in the ionic form that is present in axoplasm and extracellular fluid or ECF.
Outside the axon, the negatively charged chloride ions are neutralized in the presence of positively charged sodium ions. Negatively charged <a href="https://byjus.com/biology/proteins/">protein</a> molecules are neutralized in the presence of potassium ions within the axoplasm. The membrane of a neuron is -ve inside and +ve outside. Resting potential would be the difference in charge. The difference in charge might vary from seventy to ninety millivolts, as a result, the membrane would be polarized. Sodium potassium pump operates to keep resting potential in equilibrium.
The pump is placed on the axon membrane. Now the potassium ions are pumped from ECF to axoplasm and sodium ions are pumped from axoplasm to ECF.
The sodium-potassium pump stops operating when a stimulus is applied to a membrane of a nerve fibre. The stimulus could be either electrical, chemical or mechanical. The potassium ions rush outside the membrane and sodium ions rush inside the membrane as a result negative charges are present outside and positive charges are present inside.
The nerve fibres are either depolarized or they are said to be in the action potential. The action potential travelling along the membrane is called the nerve impulse. It is around + 30 mV. The sodium-potassium pump starts to operate once the action potential is completed. As a result, the axon membrane will obtain a resting potential by repolarization.
Now the process takes place in reverse order. It is a reversal of the process that has taken place during an action potential. Here, potassium ions will be rushed inside and sodium ions will be rushed outside. Impulse would not be transmitted through the nerve fibre during the refractory period.
In the case of white fibres, saltatory propagation takes place. That is impulse jumps from node to node and it increases with increase in the speed of nerve impulse. It is around twenty times faster compared to that of the non-medullated nerve fibres. The transmission of nerve impulse would rely upon the diameter of the fibre. For instance, the nerve impulse of a mammal is one twenty meters per second whereas nerve impulse of a Frog is 30 meters per second.
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Yogita Ingle 6 years, 10 months ago
Role of the lungs:
Lungs help in the removing waste materials such as carbon dioxide from the body.
Role of the skin:
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