Tuesday, 24 May 2011

Movement in Fish

Type of Movement
- Move Forward
- Change Direction , Brake or Stop
- Balancing

Fish has a streamllined body shape which allows it to move easily through the water with minimal frictional drag

The body of a fish is covered with scales that overlap one another with the free end pointing backwards to reduced frictional drag in the water.

The movement of fish in water is due to the antagonistic action of the W shaped segmental block of muscles (myotomes ) on both sides of the backbone and the action of its fins

Locomotion in Fish Forward Movement

During swimming, the tails is swept from side to side to bend the body on either side alternately and produce a thrust that propels the fish forward.

The sweeping of the tail is due to the contraction and relaxation of the myotome on either side of the body that work antogonistically against the backbone.

The contraction of the myotome on the right side of the body will bend the tail to the right, while the contraction of myotome on the left side of body will bend the tail to the left.

Locomotion in Fish Balancing body
The function of the fins in fish is to maintain the balance of the body during swimming.

The paired fins consists of the pectoral fins and the pelvic fins

The pectoral fins are used for steering, to change direction and as a brake to slow down or stop the movement

The pelvic fins are used for balance and to keep the fish stead by preventing driving and rolling movements.

The unpaired fins consist of one dorsal find, one ventral and one caudal fin or tail. The tail is the propulsion organ. The other unpaired fins are used for balancing by preventing rocking and rolling movement.

Tuesday, 17 May 2011

Significance of meiosis

To allow trait inheritance in offspring

To maintain diploid number in each generation

To ensure the production of haploid gamets in sexual reproduction

To produce genetic variations among offsprings

What is Meiosis

Meiosis is a very specialized process of cell division that produces gametes (eggs and sperm), and is quite distinct from the mitotic cycle of normally dividing cells

The purpose of meiosis
a) is to reduce the normal diploid cells (2 copies of each chromosome / cell) to haploid cells, called gametes (1 copy of each chromosome per cell).
In humans, these special haploid cells resulting from meiosis are eggs (female) or sperm (male).
In yeast cells, they are spores.

To carry out this specialized process, the cells duplicate their DNA but follow this by two rounds of division, instead of one. The first division separates the duplicated homologues from each other. This essentially reduces the number of chromosomes in each cell. Thus, we call this the reductional, or Meiosis I division.

The second division operates similarly to the mitotic division, and separates the sister chromatids from one another; we call this the equational, or Meiosis II division. The offspring from meiosis have half the number of chromosomes as their parent cell, because they receive just one copy of each chromosome, rather than two. (Compare the offspring in the meiosis diagram to those in mitosis).