Tag: biology

• Rotifers are multicellular, microscopic and free-living microscopic or near-microscopic multicellular pseudocoelomate animals. Hence multicellular nature and small size
• .They belong to the phylum Rotifera
• They are characterized by having specialized organ systems and a complete digestive tract that includes both a mouth and anus. Since these characteristics are all uniquely animal characteristics, rotifers are recognized as animals or metazoans, even though they are microscopic.
  
• Rotifers are called wheel animalcules because their corona is composed of several ciliated tufts around the mouth i.e ring of cilia, that in motion resemble a wheel. Hence Characteristic of rotifers is small size, ring of cilia and multicellular nature.
• So, the correct answer is 'All the above'.

Plants store complex carbohydrates as starch and animals store them as glycogen in the muscles and liver. Glycogen is the storage form of glucose in animals and humans which is analogous to the starch in plants. Glycogen is synthesized and stored mainly in the liver and the muscles. Animals do not have a cell wall but instead, have the outermost plasma membrane or cell membrane on the exterior and with well-developed organelles enclosed in membranes (eukaryotes) and are also multicellular (being made of more than one cell) and are heterotrophic as animals cannot make their own food. 

Photosystems are functional and structural units of protein complexes involved in photosynthesis, that together carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. There are 2 kinds of photosystems - photosystem I and II. In photosystem I, the reaction center is P-${ _7}$${ _0}$${ _0}$. In photosystem II, the reaction centers are P-${ _6}$${ _8}$${ _3}$. Thus, the correct answer is option A. 

P$ _{680}$ is the primary donor present in photosystem II. Structurally,  it's chlorophyll pigment dimer is present at the center of photosystem II. 680 suggests that the absorption is maximum at 680nm in red light. P$ _{680}$ or primary donor receives energy either by absorbing light or by excitation of electrons present in nearby chlorophyll. The excited electrons get captured by electron acceptor present in photosystem II, which is pheophytin and oxidized P$ _{680}$ is then reduced by electron generated from water during oxygenic photosynthesis.

Ferredoxin is the iron-containing, soluble compound in chloroplasts that helps in electron transportation and is the constituent of PS I which asses electrons to reductase complex that helps in the reduction of NADP$^+$ to NADPH which is a strong reducing agent.

Cyclic photophosphorylation is carried out by PS I only. This process takes place in stroma lamellae membrane. An external source of electrons is not required. Photolysis of water does not take place. There is no evolution of oxygen takes place because it is not connected with photolysis of water. Cyclic photophosphorylation produces ATP only. It does not involve the formation of NADPH. It operates under low light intensity, anaerobic conditions or when $CO _{2}$ availability is low. When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs, due to the cyclic flow of electrons. The membrane and lamella of the grana have both PS I and PS II, the stroma lamella membrane lack PS II as well as NADP reductase enzyme. The excited electron does not pass on to $NADP^{+}$ and is cycled back to the PS I complex through the electron transport chain.