Tag: biology

Following the key: I(a) double membrane -> II. II(a) directs growth/activities -> Nucleus (L). II(b) color -> Chromoplast (M). III(a) digests -> Lysosome (N). III(b) oxidative -> Peroxisome (O).

The biceps, also known as biceps brachii lies on the front of the upper arm between the shoulder and the elbow. The biceps brachii has two heads, or origins. Both heads originate on the scapula. The long head attaches to the supraglenoid tubercle of the scapula, which is just above the space where the humerus, or upper arm, enters the shoulder. The short head attaches to the coracoid process of the scapula. Both heads converge into one muscle, that runs the length of the humerus. The biceps brachii crosses the inside of the elbow and attaches at the radial tuberosity, which is a feature on the radius - one of the two bones (Ulna is other bone) in- the lower arm. In this way it attaches humerus with the radius and ulna. 

Muscles function is to produce force and motion. They are primarily responsible for maintaining and changing posture, locomotion, as well as movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system via peristalsis. Therefore, (b) is the correct answer. 

In mitosis DNA content is doubled during S phase resulting in 2n chromosomes having two chromatids. These 2 chromatids of 2n get arranged at metaphase plate in metaphase. And in anaphase, the 2 chromatids of 2n chromosomes are separated from each other . so the cell during this phase becomes 4n.

Early in the history of biology, scientists believed cells arose spontaneously. With the development of cell theory, people finally realized that only cells can beget other cells. In fact, two categories that define something as living or not are growth and reproduction, both of which cell division accomplishes. Cell division, also called mitosis, occurs in all living things. As living things grow, some cells die or become damaged and need replacements. Some single-celled organisms use a type of mitosis as their only form of reproduction. In multicellular organisms, cell division allows individuals to grow and change by expanding the number of total cells. The division of the nucleus is equal during cell division. This ensures the characteristic of both parent cell in daughter cells and restores the size of the nucleus.

Mitosis is equational division and meiosis is reductional division. Both consists of 4 phases, namely prophase, metaphase, anaphase and telophase. Prophase is the first phase of both mitosis and meiosis I. During this phase, the chromatin condenses and forms visible chromosomes. The mitotic spindle begins to form, nucleolus disappears, the nuclear envelope disappears. 

In sexual reproduction, an egg cell from female and a sperm from a male fuse to form a zygote, precursor to an embryo offspring. The offspring is generally distinct from parents. Both the gametes contain half the number of required chromosomes, that is they are haploid in nature. The zygote contains the exact number of chromosomes required. This is how chromosome number is conserved from generation to generation. The zygote undergoes further cell division to form an embryo. 

1. In G$ _1$  phase the amount of DNA is the same as 40 because the cell is metabolically active but no division of DNA is observed.
   
2. In G$ _2$ phase the DNA gets doubled as it has gone through the synthesis phase which is characterized by the replication of DNA.
3. In mitosis since equational division occurs the DNA content remain 4C through the process before the transfer of DNA into daughter cells.

G$ _1$ , S , G$ _2$, M , cytokinesis. The correct sequence has G$ _1$ as a preparation for S and G$ _2$ as the time between the completion of S and entry into M. Cytokinesis occurs after the other stages to create two daughter cells.