The counter current mechanism operating inside the kidney is the main adaptation for the conservation of water. There are two counter current mechanisms inside the kidneys. They are Henle’s loop and vasa rectae.
Henle’s loop is a U-shaped part of the nephron. Blood flows in the two limbs of the tube in opposite directions and this gives rise to counter currents. The Vasa recta is an efferent arteriole, which forms a capillary network around the tubules inside the renal medulla. It runs parallel to <st1:place w:st="on">Henley</st1:place>’s loop and is U-shaped. Blood flows in opposite directions in the two limbs of vasa recta. As a result, blood entering the renal medulla in the descending limb comes in close contact with the outgoing blood in the ascending limb.

The first phase of mitosis within M phase is called prophase. It follows G2, the final phase of interphase. A cell entering M phase manifests a number of physicsl signs. ... Chromosome condensation is visible through a microscope and is required for subsequent chromosome separation during later stages of mitosis. During the mitotic (M) phase, the cell divides its copied DNA and cytoplasm to make two new cells. M phase involves two distinct division-related processes: mitosis and cytokinesis. ... Mitosis takes place in four stages: prophase (sometimes divided into early prophase and prometaphase), metaphase, anaphase, and telophase.

The process of photosynthesis takes place in the green leaves of a plant. The carbon dioxide gas required for making food is taken by the plant leaves from the air which enters the leaves through tiny pores called stomata. Water required for making food is taken from the soil which is transported to the leaves from the soil through the roots and the stem. The sunlight provides energy required to carry out the chemical reactions involved in the preparation of food. The green pigment called chlorophyll absorbs sunlight energy.

The photosynthesis takes place in three steps:
(i) Absorption of sunlight energy by chlorophyll.
(ii) Conversion of light energy into chemical energy and splitting of water into hydrogen and oxygen by light energy.
(iii) Reduction of carbon dioxide by hydrogen to form carbohydrates like glucose by utilising the chemical energy.

1. Epithelial Tissue:

It is the simplest tissue and protective in nature. The cells of this tissue are tightly packed and they form a continuous sheet. They contain a very little or no intercellular space. It covers most organs and cavities within the body. The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue. Anything entering or leaving the body crosses at least one layer of epithelium. As a result, the permeability of the cells of various epithelia plays an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body. All the epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.

Modification for food storage: The underground stems of potato, ginger, turmeric, zamikand, Colocasia, etc. are modified for food storage. Such modifications are the tools of perenation to tide over unfavourable conditions.
Modifications for climbing: In some plants, stem tendrils develop form axillary buds. These are slender and spirally coiled structures. A tendril helps the plant to climb to a support, e.g. cucumber, pumpkin, grapevine, etc.
Modification for defence: In some plants, the axillary buds are modified into woody, straight and pointed thorns. Such thorns protect the plant from browsing animals, e.g. Citrus, Bougainvillea.
Modification for photosynthesis: In some plants of arid regions, the stems are modified into flattened or fleshy cylindrical structures. The flattened structure can be seen in Opuntia and the cylindrical structure can be seen in Euphorbia. Such structures contain chlorophyll and photosynthesis happens in them.
Modification for vegetative propagation: Stems are modified for vegetative propagation in many plants, e.g. grass, berry, dahlia, etc.

On a hot sunny day, the enzyme RuBisCo carries out the oxygenation of RuBP instead of carboxylation. The compound formed is 2- phosphoglycolate which is finally converted into 3-phosphoglyceric acid with the release of oxygen. This process is known as photorespiration. The site for photorespiration is chloroplast, peroxisome and mitochondrion. Photorespiration occurs because the active site of RuBisCo for carboxylation and oxygenation is the same. At high temperature, concentration of dissolved carbon dioxide in equilibrium with air decreases more than cocentration of oxygen which favors oxygenation. Thus, at high temperature RuBisCo functions as a oxygenase and instead of fixing carbon dioxide, oxidises ribulose 1,5-bisphosphate to produce a 3-carbon phosphoglyceric acid and a 2-carbon phosphoglycolate. Phosphoglyceric acid is used up in Calvin cycle.  

Muscles are the structures which in coordination with bones bring about movement in an organ. Muscle contraction is clearly explained by sliding-filament theory. Muscles are made up of 2 types of proteins namely Actin and Myosin filaments.

•  Muscle starts to contract when it receives information from motor neurons.
•  Neuromuscular junctions are formed by the junctions between motor neuron and sarcolemma of individual muscle fibre.
•  As the neural signal reaches neuro-muscular junction, acetyl choline is released at this place.
•  Acetyl choline causes an action potential in the sarcolemma and releases calcium ions in the sarcoplasm.
•  Calcium ions bind to the troponin of the actin and bring a change in its structure. This causes a movement in tropomyosin.
•  This structural change exposes myosin binding sites on actin filaments. Myosin binds to actin forming a cross bridge.
•  These cross bridges pull the attached actin to the centre of the A band. Z-line is also pulled inwards. This causes shortening of sarcomere which is termed as muscle contraction.
•  During contraction, I bands are reduced, A bands retain their length. Actin and myosin filaments slide over one another during contraction.
•  Myosin releases ADP and pi and returns to its original state. New ATP binds to myosin head and the cross bridge is broken.
•  Myosin head hydrolyses ATP to form a cross bridge.
•  These events are repeated till calcium ions return into sarcoplasmic reticulum. Calcium ions are released till acetyl choline is present. Acetyl choline is released till the muscle fibre receives signal from motor neurons.

The pelvic region is the area between the trunk — or main body — and the lower extremities, or legs. The male pelvis is different from a female’s. The pelvic bones are smaller and narrower. Evolutionary scientists believe this stems from man’s hunter roots, as a leaner pelvis made running easier.

Meiosis involves two sequential cycles of nuclear and cell division, but only a single cycle of DNA replication. Meiosis is divided into meiosis I and meiosis II.

• Meiosis I begins after the S phase, and meiosis II follows meiosis I.
• Pairing of homologous chromosomes happens during meiosis which results in recombination of genes.
• Four haploid daughter cells are formed at the end of meiosis.

Phycobiont refers to the algal component of the lichens and mycobiont refers to the fungal component. Both of these are present in symbiotic relationship in which Algae prepare food for Fungi due to presence of chlorophyll whereas the fungus provides shelter to algae and absorbs water and nutrients from the soil.

The process by which green plants make their own food from carbon-dioxide and water in the presence of sunlight and chlorophyll is called photosynthesis.