Zoology - 3 (B. Sc. Agriculture)

Teh cell wall remains present only in plant celsl. It is totally absent in animals.

A holoblastic cleavage producing blastomeres of equal size

Yes, the  threatened species are those which are suffering from the danger of extinction. An endangered species is a population of organisms which is at risk of becoming  extinct because it is either less in number or threatened by changing environmental or predation parameters, e.g. blue whale, tiger, bonobo, gaint panda etc.

Amphibian eggs are mesolecithal (moderate amount of yolk) and telolecithal (yolk concentrated at one pole). They undergo unequal holoblastic cleavage, where the entire egg divides but into unequal-sized cells due to yolk distribution. This contrasts with other egg types in the options.

Mitochondria contain their own circular DNA molecule (mtDNA), separate from nuclear DNA. This mitochondrial DNA encodes proteins essential for the organelle's role in ATP production. The other organelles listed (golgi apparatus, ribosomes, vacuoles) do not contain DNA.

In cartilaginous fish (Chondrichthyes like sharks and rays), the mouth is positioned ventrally on the underside of the head. This is a key anatomical difference from bony fish (Osteichthyes), which typically have terminal mouths at the anterior end. Jawless fish and ray fish are not the correct classification for this characteristic.

The pituitary is often called the master gland because the hormones it secretes play an active part in controlling the activities of all the other endocrine glands. This impressive power is wielded from two little bumps at the base of the brain, about midway between the ears at eye level.

insects 
 The Malpighian tubule system is a type of excretory and osmoregulatory system found in some Uniramia (Insects and Myriapoda),

Butterflies belong to the order Lepidoptera.

During anaphase I, homologous chromosomes are pulled from each other and move to opposite poles.

Anopheles mosquito is the vector of malaria.

Chitin is a nitrogen-containing polysaccharide composed of N-acetylglucosamine units. The nitrogen comes from the acetyl group attached to each sugar molecule. Simple polysaccharides (like starch) contain only carbon, hydrogen, and oxygen, while chitin's nitrogen makes it chemically distinct and structurally stronger.

A goitre is a swelling of the neck or larynx resulting from enlargement of the thyroid gland (thyromegaly), associated with a thyroid gland that is not functioning properly. The main reason is deficiency of iodine in the diet which is required for the synthesis of thyroid hormones.

 Malaria, filaria and yellow fever are caused by mosquitoes.

Basophils are the white blood cells primarily responsible for releasing histamine and heparin. Histamine promotes inflammation and allergic responses, while heparin acts as an anticoagulant that prevents blood clotting. Neutrophils are phagocytic, eosinophils combat parasites, and monocytes become macrophages.