Biology Test 29

Fructose is laevorotatory. Laevorotatory compounds are those which rotate the plane of polarized light to the left. Glucose is dextrorotatory on the other hand.

Fehling’s solution reacts with the reducing sugars having free aldehyde group like glucose. It gives a red precipitate indicating the presence of carbohydrate.

In animal cells, during synthesis or S-phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm. During this time, the amount of DNA per cell doubles. However, there is no increase in the chromosome number.

Diakinesis is the last stage in prophase of Meiosis, in which the nucleolus and nuclear envelope disappear, spindle fibres form, and the chromosomes shorten in preparation for anaphase. It can be best seen in flower bud .

Onion root tip, Lead of dichanthium consists of meristamatic cells which divide by mitosis. Therefore, no diakinesis is observed.

Endo mitosis is the mitosis takes place without dissolution of the nuclear membrane, and not followed by cytoplasmic division, resulting in doubling of the number of chromosomes with in the nucleus.

mitosis is the common method of cell division. It takes place in the somatic cells. It is also called the somatic division. It was first observed by strasburger in 1875. His works in 1876, a book name “on cell formation and cell division” set forth basic principles of mitosis.

prophase is the longest stage in mitosis. During prophase, the cell nucleus becomes spheroid, and increase in viscosity of cytoplasm, the chromosomes are visible as long thin threads. Towards the end of prophase, each chromosome is seen to consist of 2 chromtids held together by the centromere.

J. David Robertson (1959) proposed the “Unit membrane model”. It has a thickness of about 7.5 nm with a central lipid layer of 3.5 nm thick and two peripheral protein layers of 2.0 nm each.

peroxisomes contains oxidative enzymes , such as catalase and oxidase. These are small spherical bodies about the size of lysosomes .The catalase enzymes of peroxisomes convert hydrogen peroxide to water and oxygen.

The lampbrush chromosomes are found in oocytes of many vertebrates (Amphibian, reptiles and birds) and some invertebrates (insects). They also occur in the giant nucleus of the unicellular algae Acetabularia.