If a plant cell is kept in hypertonic solution, water comes out from the cell sap due to exosmosis. Water loss from the cell sap results in contraction of protoplast, which is referred to as plasmolysis. The cell is surrounded by the hypertonic solution, and the cell wall allows entry of most of the solutions. The hypertonic solution enters the cell wall freely but is not allowed to cross the cell membrane. 

Thus, the space between the cell wall and condensed protoplast is filled with hypertonic solution in a plasmolyzed cell.

Keys are used to identify different species. A key will usually ask questions based on easily identifiable features of an organism. Dichotomous keys use questions to which there are only two answers. They can be presented as a table of questions, or as a branching tree of questions.

Branching tree example

This tree could help you identify a new vertebrate. For example, if it had no fur or feathers and dry skin, you would follow the right-hand pathway at the first and second junctions, but the left-hand pathway at the third junction. This would lead you to identify the animal as a reptile.

Insectivorous means insect-eating, these plants derive most of their nutrition from the insects, that they trap and consume. These plants grow in humid areas, where plenty of sunlight and moisture is found. They are found in the nitrogen deficient soil. That is why they trap and digest insects to absorb nutrients. Venus flytrap, pitcher plant and cobra lily are some of the insectivorous plants’ names. They are often called Carnivorous plants.

• Chemicals or molecules present in the living organism are known as biomolecules. Biomolecules are divided into two types- inorganic and organic.
• Inorganic biomolecules includes minerals, gases and water and organic biomolecules includes carbohydrates, fats, proteins, nucleic acids, vitamins, etc.

The taxonomic aids are the aids which help in identification, classification and naming of a newly discovered organisms (plant or animal). It could be in the form of preserved document like herbaria or specimen kept at museums or scientific institutions. Taxonomical aids are Techniques, Procedures and Stored information that are helpful in identification and classification of organisms. Herbarium, Botanical gardens, Museum, Zoological parks and Key are examples of Taxonomical Aids.

Mesosome is a convoluted membranous structure formed in a prokaryotic cell by the invagination of the plasma membrane. Its functions are as follows:

(1) These extensions help in the synthesis of the cell wall and replication of DNA. They also help in the equal distribution of chromosomes into the daughter cells.

(2) It also increases the surface area of the plasma membrane to carry out various enzymatic activities.

(3) It helps in secretion processes as well as in bacterial respiration.

The presence or absence of pigments is the main basis of classification of algae. Chlorophyceae: Chlorophyll a and b are present in them and impart green colour. Chlorophyceae are also called 'blue-green algae'. Phaeophyceae: Chlorophyll a and c and fuxoxanthin are present.

Prophase is the first phase of mitosis, the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. During prophase, the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses. During prophase I, the homologous chromosomes condense and become visible as the x shape we know, pair up to form a tetrad, and exchange genetic material by crossing over. During prometaphase I, microtubules attach at the chromosomes' kinetochores and the nuclear envelope breaks down.

Metaphase is a stage of the cell cycle occurring in both mitosis and meiosis cell division processes. During metaphase in mitosis and meiosis, the chromosomes condense and they become visible and distinguishable during alignment at the center of the dividing cell, to form a metaphase plate at the center of the cell. In metaphase, chromosomes are lined up and each sister chromatid is attached to a spindle fiber. In anaphase, sister chromatids (now called chromosomes) are pulled toward opposite poles. In telophase, chromosomes arrive at opposite poles, and nuclear envelope material surrounds each set of chromosomes.

The synaptonemal complex (SC) is a protein structure that forms between homologous chromosomes (two pairs of sister chromatids) during meiosis and is thought to mediate synapsis and recombination during meiosis I in eukaryotes. Prophase 1 of Meiosis is the first stage of meiosis and is defined by five different phases; Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.

Prophase immediately follows S and G2 phase of the cycle and is marked by condensation of the genetic material to form compact mitotic chromosomes composed of two chromatids attached at the centromere.

The completion of prophase is characterised by the initiation of the assembly of the mitotic spindle, the microtubules, and the proteinaceous components of cytoplasm that help in the process.

The nuclear envelope starts disintegrating.

meiosis 1 Prophase 1

(1) Leptotene – The chromosomes begin to condense and attain a compact structure during leptotene.

(2) Zygotene – In zygotene, the pairing of homologous chromosomes starts a process known as chromosomal synapsis, accompanied by the formation of a complex structure called synaptonemal complex. A pair of synapsed homologous chromosome forms a complex known as bivalent or tetrad.

(3) Pachytene – At pachytene stage, crossing over of non-sister chromatids of homologous chromosomes occurs at the recombination nodules. The chromosomes remain linked at the sites of crossing over.

(4) Diplotene – Diplotene marks the dissolution of the synaptonemal complex and separation of the homologous chromosomes of the bivalents except at the sites of cross-over. The X-shaped structures formed during separation are known as chiasmata.

(5) Diakinesis – Diakinesis is marked by the termination of chiasmata and assembly of the meiotic spindle to separate the homologous chromosomes. The nucleolus disappears and the nuclear envelope breaks down.

Zygotene

The zygotene stage, otherwise called zygonema, from Greek words signifying "matched threads", happens as the chromosomes approximately line up with one another into homologous chromosome pairs. In some organisms, this is known as the bouquet stage as a result of the manner in which the telomeres bouquet toward one side of the core. At this stage, the synapsis of homologous chromosomes happens, encouraged by gathering of the central component of the synaptonemal complex. Pairing is achieved in a zipper-like style and may begin at the centromere (pro-centric), at the chromosome ends (terminal), or at some other portion. Individuals of a pair are equivalent long and in the position of the centromere. Therefore, pairing is very specific and definite. The paired chromosomes are known as bivalent or quadruplicate chromosomes.

Pachytene

The pachytene stage, otherwise called pachynema, from Greek words signifying "thick threads". At this point, a quadruplicate of the chromosomes has framed known as a bivalent. This is the phase when homologous recombination, including chromosomal hybrid (traverse), happens. At this stage, the Non-sister chromatids of homologous chromosomes may exchange segments over regions of homology. 

Anaphase I

Kinetochore microtubules become short, pulling homologous chromosomes (which comprise of a couple of sister chromatids) to opposite poles. Nonkinetochore microtubules extend, pushing the centrosomes separated apart. The cell stretches for division down the center. Unlike in mitosis, just the cohesin from the chromosome arms is degraded while the cohesin encompassing the centromere stays secured. This enables the sister chromatids to stay together while homologs are segregated.

he mitotic apparatus consists of centrioles with the centre-spheres surrounding them, a cell division spindle with a system of microtubules, and an intermediate substance. Depending on the degree of development of astral rays around the centre-sphere, the mitotic apparatus is classified as astral (characteristic of most animal cells) or anastral (characteristic of plant cells). The mitotic apparatus is formed from macromolecules present in the interphase cell and from material synthesized before division. Its main components are ribonucleoproteins (about 90 percent proteins and 6 percent ribonucleic acid [RNA]). It also contains polysaccharides, lipids, and adenosine triphosphatase.

• Genetic stability- Mitosis helps in the splitting of chromosomes during cell division and generates two new daughter cells. Therefore the chromosomes form from the parent chromosomes by copying the exact DNA.  Therefore, the daughter cells formed as genetically uniform and identical to the parent as well as to each other. Thus mitosis helps in preserving and maintaining the genetic stability of a particular population.
• Growth- Mitosis help in increasing the number of cells in a living organism thereby playing a significant role in the growth of a living organism.

It is a protein complex, visible with the electron microscope, that is the physical basis of the pairing of homologous chromosomes (synapsis) during meiosis. It assembled during zygotene as homologous chromosomes pair up, and it is disassembled during diplotene as homologous chromosomes separate.

<button aria-label="like this post" title="like this post"></button>

S phase – It is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per cell) doubles, but the chromosome number remains the same.

G2​ phase – In this phase, the cell continues to grow and prepares itself for the division. The proteins and RNA required for mitosis are synthesised during this stage.

Osmolarity defines the solute concentration, i.e. number of moles of solute that contributes to the osmotic pressure of a solution.
Osmolarity can be expressed in milli osmol per litre or mOsmol L^-1  
 

• The arrangement of ovules within the ovary is known as placentation.
• The placentation is of different types namely, marginal, axile, parietal, basal, central and free central.
• In marginal placentation the placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows. Example- pea

Chromosomes are thread-like structures present in the nucleus, which carries genetic information from one generation to another. They play a vital role in cell division, heredity, variation, mutation, repair and regeneration.

Based on the number of centromeres present

1. Monocentric: having only one centromere
2. Holocentric: having diffused centromere and microtubules are attached along the length of a chromosome
3. Acentric: chromosome may break and fuse together to form a chromosome without a centromere. It cannot attach to the mitotic spindle
4. Dicentric: chromosomal aberration where chromosomes break and fuse together with two centromeres. They are also unstable as two centromeres tend to migrate to opposite poles resulting in fragmentation

The nucleus is a sphere-shaped organelle found in eukaryotic cells. It contains the genetic material of the cell in the form of nucleic acids. It is responsible for controlling all activities of the cell. and contains a nuclear membrane, chromosomes, nucleolus and nucleoplasm.

The Endomembrane system is a membranous component of the eukaryotic cell. The cytoplasm of the cell contains a system of membranous organelles that are suspended in it. The organelles are termed as a system even though they have different structures and functions as they are essential to the working of the cell. All these organelles work in coordination and they include the cell membrane, vacuoles, the nuclear membrane, lysosomes, Golgi complex, vesicles and the endoplasmic reticulum (ER).