Beta cells of islets of Langerhans secrete insulin. If the beta cells are damaged then no insulin will be secreted hence, the sugar level of the blood will rise and may lead to Diabetes mellitus.  

Abscissic acid

(a) Four characteristics that have developed during human evolution are:

(i) Erect Posture with four reused curves in the spine.

(ii) An upright head having eyes facing in front.

(iii) Straight limbs with arms shorter than legs.

(iv) Fingers and toes had flat nails in place of claws.
(b) Stem cells are undifferentiated cells of a multicellular organism which are capable of giving rise to indefinitely more cells of the same type, and from which certain other kinds of cell arise by differentiation.are characterised by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialised cell type.

• Stem cells are being used in cancer therapy. 

• Stem cell is used to make different muscles. 
(c) In situ conservation means maintaining plant diversity in natural reserves it protects the species threatened with loss or Extinction, supply materials to restore degraded lands and provide materials for genetic improvement of crop plants. It is mostly done by establishing biosphere reserves.

Ex situ conservation crucial Besides the primary repositories for wild plants, botanical gardens have a crucial role both in conservation and education.

Gene Banks: A gene bank is an institution where valuable plant material likely to become irretrivably lost in the wild or in cultivation is preserved in a viable condition gene bank consume stocks of both seeds and vegetative material. The stored germplasm not only safeguard the species threatened with loss or extinction but is also actively utilized the world over by breeds to develop novel varieties.
Cryopreservation - Cryopreservation (preservation in liquid nitrogen, -196°C) of plant germplasm. The term 'cryopreservation' (cryogenic preservation) refers to the storage of cells, tissues and organs at the ultra-low temperature of liquid nitrogen (-196°C).

Genetic engineering is that branch of biotechnology. This is a process in which the alteration of the genetic makeup of cells is done by deliberate and artificial means. This process involves transfer or replacement of genes to create recombinant DNA. This can be done by cutting DNA molecules at specific sites to get fragments containing desirable and useful genes from one type of cell. Thereafter, these genes can be inserted into a suitable carrier or vector. Now, the recombinant DNA can be put into a foreign cell of a bacterium or plant or animal cell.

By this technique they acquire useful characteristics, such as disease resistance or to make useful enzymes, hormones, vaccines, etc.

The three tools for recombinant DNA technology are as follows :

1. Cell culture containing cells with the desired DNA segment (gene).

2. DNA modifying enzymes such as (a) Restriction endonuclease from various bacteria (b) DNA ligase from Escherichia coli which joins DNA molecules (c) DNA polymerase from E. coli.

3. Cloning vectors. The desired gene is inserted in the vectors or gene carrier to form DNA.