General Biology - Plants, Animals & Human Physiology

The control of nuclei over the phenotypic expression of the cell was studied in Acetabularia.

Ergosterol is a biological precursor (a provitamin) to vitamin D₂. It is turned into viosterol by ultraviolet light and is then converted into ergocalciferol which is a form of vitamin D. It does not occur in plants or animal cells, but it is a component of yeast and fungal cell membranes serving the same function that cholesterol serves in animal cells.

The vascular bundles of a monocot stem are collateral and closed.

Roots of varying shapes are present at the nodes of the running stem.

Torpedo generates electric current.

Nyctalopia or night blindness (inability to see in dim light) is a disease caused due to the lack of vitamin A.

Colchicine is used to induce polyploidy in plants.Polyploid cells and organisms are those containing more than two paired (homologous) sets of chromosomes.

Sea cucumber does not belong to phylum coelenterata. It belongs to phylum echinodermata. 

Blood vessels leading into Bowman's capsule are called afferent arterioles and discharge blood into an efferent arteriole. Because the calibre of the efferent arteriole is smaller than that of the afferent arteriole, a resistance to blood flow out of the golmeruli is developed. As a result, a golmerular hydrostatic pressure builds up in the glomerulus. 

Peripatus is a connecting link between Annelida and Arthropoda, because it exhibits characterstics of phylum Annelida and Arthropoda.
(A)        Annelidan characters
(a)        Presence of nephridia as excretory organ.
(b)        Body pseudosegmented and worm-like
(c)        Presence of simple eyes.
(d)        Thick cuticle
(B)       Arthropod Characters
(a)       Clawed and pseudosegmented walking legs
(b)       Presence of trachea as respiratory organs
(c)       Presence of antennae
Pertipatus shows that arthropods have evolved from annelid ancestors.

The homologous chromosomes pair up and form synaptonemal complex during this phase.

The growth of a pollen tube toward the ovule is an example of chemotropism - movement in response to chemical stimuli. The ovule releases chemical signals (specifically calcium ions and chemotropic factors like LURE peptides) that guide the pollen tube's growth. This ensures precise delivery of sperm cells to the embryo sac for fertilization.

In Brassica campestris (mustard plant) and most angiosperms, the endosperm is triploid (3n). This results from double fertilization, where one sperm fertilizes the egg (forming a 2n zygote) and the second sperm fuses with the two polar nuclei (each n), creating a 3n endosperm that provides nutrition to the developing embryo.

In unisexual plants, sex expression can be modified by applying plant growth regulators, particularly auxins and ethylene. These hormones can influence the development of male or female flowers. For example, applying auxins or ethylene often promotes femaleness in certain species, while gibberellins may promote maleness.