Biology Test-13

Asexual reproduction in Penicillium takes place by unicellular, uninucleate, non-motile spores, the conidia; formed on conidiophore. A number of flask-shaped phialides or sterigmata develops at the tip of each metulae.

In Fungi, asexual reproduction occurs through spores. These are the specialised structure which separates from the organism, dispersed, and germinate to produce new mycelium on falling on a suitable substrate. Various means of asexual reproduction are: 

Conidia: They are the non-motile, thin-walled non-motile exogenous spores produced at the tips of erect hyphae called conidiospores. Example: Penicillium

Zoospores: In fungi, especially aquatic membrane produces these types of spores. It may be uniflagellate as in Synchytrium or biflagellates as in Saprolegnia.

Sporangiospores: They are thin-walled non- motile spores produced endogenously in sporangium during favourable conditions. Example: Rhizopus and Mucor

Chlamydospore: In some fungi, during unfavourable condition Hyphae forms a thick-walled resting resistant spore. On the return of favorable condition, they germinate to give rise to a new individual. E.g. Rhizopus

There can be 36 ATP molecule during aerobic respiration of one molecule of glucose.

The NADH₂ molecule produced during glycolysis cannot enter directly into mitochondria. This entry of glycolytic energy inside mitochondria is performed either by using the glycerol-3-phosphate shuttle or by Malate- asparate shuttle. These shuttles do not occur in prokaryotes.

Glycerol 3 phosphate shuttle: It explains that there is a loss of 1 ATP for each cytosolic NADH⁺ H⁺. Net ATP produced in respiration is 36 instead of 38 ATP. It occurs in flight muscles cells and brains.

Malate-aspartate shuttle: It occurs in heart, kidney and other organs. 38 ATP is produced as a net in aerobic respiration.

Therefore, total net gain ATP = 36 or 38 depending upon the type of shuttle system used in aerobic respiration.

The transfer of pollen grains from the stamens, the flower parts that produce them, to the ovule-bearing organs or to the ovules, is termed as Pollination.

It occurs when pollen is moved within flowers or carried from flower to flower by pollinating animals such as birds, bees, bats, butterflies, moths, beetles, or other animals, or by the wind.

Pollination through birds is termed as Ornithophily.

The anther is a terminal bilobed structure and the wall of the anther consist of the following layers:

Endothecium: The cell of the endothecium layer has α-cellulosic fibrous bands arising from the inner tangential wall which help in the dehiscence of anther due to its hygroscopic nature. They are absent in hydrophytes.

Epidermis: It is the outermost, singled layered and protective function. The epidermis of Arceuthobium(parasite) develops some fibrous thickenings and is called exothecium.

Middle layer: Cells of this layer are ephemeral and are 1 to 3 layered, which degenerate at maturity.

Tapetum: It is the innermost layer of the anther wall which surrounds the sporogenous tissue. It nourishes the developing pollen grains. The cell of this layer possess dense cytoplasm and generally have more than 1 nucleus and show an increase in DNA content.

Diploid endosperm is found in Oenothera.

The Endosperm is the tissue produced inside the seeds of most flowering plants following fertilization. It is a product of triple fusion, develops from the central cell of the embryo sac. It is generally Triploid tissue. Date palm, Ivory palm and Castor have triploid endosperm. Diploid endosperm is found in Oenothera.

Seeds in general, are the product of fertilization, a few flowering plants such as Asteraceae and grasses have evolved a special mechanism to produce seeds without fertilization is called Apomixis.It is a form of asexual reproduction that mimics sexual reproduction. It is of two types:

a) Adventive Embryony: It arises from the diploid saprophytic cell such as nucellus or integuments. 

b) Recurrent Agamospermy: In this, diploid embryo sac is formed from megaspore mother cell which has the diploid egg which develops into the diploid embryo.

Example: Pear and Apple.

The natural methods of vegetative reproduction in stem include:

1. Offsets: Short horizontal branch producing a cluster of leaves above and the clusters of roots below.

e.g. Water hyacinth

2. Aerials shoot: Each segment of the stem having at least one node can form new plants

e.g. Opuntia

3. Rhizome: It is the main underground perennial stem buds present on the nodes take part for the formation of the new aerial shoot during the favourable season of growth.

e.g. Ginger

4. Bulbils: these are large size fleshy buds which are specialized for vegetative propagation

e.g. In agave bulbils are modified buds develop on the floral axis.

Bryophyllum has adventitious buds arise from notches present at the margin of leaves that help in vegetative reproduction.

Chara is a monoecious plant, as both male and female reproductive structures are in the same organisms.

In flowering plants, both male and female flowers occur in the same individuals. These plants are called monoecious plants.

Unisexual flowers are incomplete flowers, containing either male or female reproductive organs in the flower. That means, androecium, which is the male reproductive structure and gynoecium, which is the female reproductive structure, are found in separate flowers.

Heterothallic and dioecious is the term used to describe the unisexual condition.

In dioecious plants, either male or female flowers may occur.

Sexual flowers are complete flowers, containing both androecium and gynoecium in one flower. Therefore, bisexual flowers contain both stamens and pistils in the same flower. So, bisexual flowers are called hermaphrodite or androgynous flowers as well.

Archaebacteria is the oldest living organisms on earth. They are prokaryotes and unicellular. The cell membrane contained branched-chain lipids, decrease membrane fluidity. They are mostly obligate anaerobes.

Their cell wall is made up of complex polysaccharides and the complex polypeptide that differ from other bacteria having a different cell wall.

This composition of the cell wall is responsible for survival in extreme conditions .This is thought to be because the early Earth’s atmosphere was filled with poisonous gases and was very hot – nothing could survive, except the archaebacteria.

There are three phyla, or groups, of archaebacteria: Methanogens, Halophiles and Thermoacidophiles.

Haemophilia is an inherited genetic condition, that means it passed down through families.

Each person inherits two sex chromosomes from their parents. Females have two X chromosomes. Males have one X and one Y chromosome.

The person suffering from this diseases cannot synthesize the normal blood protein called anti-haemophilic globulin(AGH) which is required for the normal clotting.

This gene is located on X chromosomes and is recessive, and remain latent in the carrier females. Thus, only a single protein is involved in the clotting of blood is affected.

Auxin was the 1st hormones to be discovered and isolated from the human urine samples because auxins do not have a metabolic role so excreted out of the body. It mainly occurs in growing apices of the stems and roots from where they can migrate to their site of actions.

Physiological effects:

• It is responsible for the initiation and promotion of the cell division in the cambium.
• It also controls the xylem differentiation.
• Abscission
• Apical dominance

In photosynthetic carbon fixation, magnesium ion (Mg²⁺) is an activator for both ribulose bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase enzymes. The magnesium ions help to maintain the pH and helps in the activation of enzymes.

During mRNA synthesis, the unwanted DNA regions are removed and amino acid coding regions are joined by the process of splicing.

Capping: The process of addition of an unusual nucleotide, 7 methyl guanosine to the 5' end of the hnRNA is called capping. It forms a cap-like structure on the 5' end of hnRNA.

Tailing: The process of addition of 200-300 nucleotides of adenylic acid to the 3' end of hnRNA is called tailing. This tail is called poly-A tail.

Splicing: After capping & tailing now the hnRNA undergoes a process where the non-coding regions, introns are removed and the coding region exons are joined together to form the functional mRNA by the process called splicing.

The removal of introns is done with the help of the ribonuclease enzyme and the exons are joined with the help of enzyme DNA ligase.

Starting codon of m-RNA is near P site of ribosomes and next codon is near A site, so t-RNA with formyl methionine amino acid first attaches to P site of ribosomes and next codon is near A site.

The link between the amino acid of P site of tRNA is broken and t RNA of P site is discharged so COOH of P sites amino acid become free. Now the peptide bond takes place between taking places between COOH groups of P site amino acid NH₂ groups at A site amino acid.

In prokaryotes with the help of SD sequence, mRNA recognise the smaller subunit of the ribosome. In smaller subunit of the ribosome, the complementary sequence of SD is present on 16 “s” rRNA, called ASD sequence. Therefore mRNA recognise the smaller subunit of the ribosome with the help of both SD and ASD sequence.

The UTRs are present on mRNA at both 5’ end and at 3’ end, which is required for the efficient translation process recognising the smaller subunit of the ribosome by mRNA

Methionine is specified by the codon AUG, which is also known as the start codon. Consequently, methionine is the first amino acid to dock in the ribosome during the synthesis of proteins. Tryptophan is unique because it is the only amino acid specified by a single codon. The remaining 19 amino acids are specified by between two and six codons each.