What is Ecological Succession? also write examples and type of ecological succession.

Question: 

What is Ecological Succession? also write examples and type of ecological succession.

Answer:

Ecological succession is the steady and gradual change in a species of a given area with respect to the changing environment. It is a predictable change and is an inevitable process of nature as all the biotic components have to keep up with the changes in our environment.

The ultimate aim of this process is to reach equilibrium in the ecosystem. The community that achieves this aim is called a climax community. In an attempt to reach this equilibrium, some species increase in number while some other decrease.

In an area, the sequence of communities that undergo changes is called sere. Thus, each community that changes is called a seral stage or seral community.

All the communities that we observe today around us have undergone succession over a period of time since their existence. Thus, we can say that evolution is a process that has taken place simultaneously along with that of ecological succession. Also, the initiation of life on earth can be considered to be a result of this succession process.

If we consider an area where life starts from scratch by the process of succession, it is known as primary succession. However, if life starts at a place after the area has lost all the life forms existing there, the process is called secondary succession.

It is obvious that primary succession is a rather slow process as life has to start from nothing whereas secondary succession is faster because it starts at a place which had already supported life before. Moreover, the first species that comes into existence during primary succession is known as pioneer species.

Types of Ecological Succession

These are the following types of ecological succession:

Primary Succession

Primary succession is the succession that starts in lifeless areas such as the regions devoid of soil or the areas where the soil is unable to sustain life.

When the planet was first formed there was no soil on earth. The earth was only made up of rocks. These rocks were broken down by microorganisms and eroded to form soil. The soil then becomes the foundation of plant life. These plants help in the survival of different animals and progress from primary succession to the climax community.

If this primary ecosystem is destroyed, secondary succession takes place.

Secondary Succession

Secondary succession occurs when the primary ecosystem gets destroyed. For eg., a climax community gets destroyed by fire. It gets recolonized after the destruction. This is known as secondary ecological succession. Small plants emerge first, followed by larger plants. The tall trees block the sunlight and change the structure of the organisms below the canopy. Finally, the climax community arrives.

Cyclic Succession

This is only the change in the structure of an ecosystem on a cyclic basis. Some plants remain dormant for the rest of the year and emerge all at once. This drastically changes the structure of an ecosystem.

Seral Community

“A seral community is an intermediate stage of ecological succession advancing towards the climax community.”

A seral community is replaced by the subsequent community. It consists of simple food webs and food chains. It exhibits a very low degree of diversity. The individuals are less in number and the nutrients are also less.

There are seven different types of series:

Examples of Ecological Succession

Following are the important examples of ecological succession:

Acadia National Park

This national park suffered a huge wildfire. Restoration of the forest was left to nature. In the initial years, only small plants grew on the burnt soil. After several years, the forest showed diversity in tree species. However, the trees before the fire were mostly evergreen, while the trees that grew after the fire were deciduous in nature.

Ecological Succession of Coral Reefs

Small coral polyps colonize the rocks. These polyps grow and divide to form coral colonies. The shape of the coral reefs attracts small fish and crustaceans that are food for the larger fish. Thus, a fully functional coral reef exists.

Write Dicotyledonous and Monocotyledonous Leaves.

Question: 

Write Dicotyledonous and Monocotyledonous Leaves.

Answer:

Dicotyledonous and Monocotyledonous Leaves

Dicot Leaf

Dicotyledonous leaf shows reticulate venation.

• Lamina consists of epidermis, mesophyll and vascular system.
• The epidermis is covered by cuticle and stomata; abaxial epidermis (lower surface) possesses more stomata than adaxial epidermis (upper surface). Sometimes adaxial epidermis lack stomata.
• Mesophyll, (parenchymatous cells) composed of the palisade and spongy parenchyma is present in between the adaxial epidermis and abaxial epidermis.
• The chloroplasts present in mesophyll perform photosynthesis in leaves.
• Vascular bundles are surrounded by bundle sheath cells and form the veins and midrib.

Monocot Leaf

Monocotyledonous leaves are characterized by parallel venation. The anatomy of a monocot leaf includes:

• Both adaxial epidermis and abaxial epidermis bear stomata.
• There is no differentiated palisade and spongy parenchyma of the mesophyll.
• Bulliform cells are present, which is developed from adaxial epidermal cells and the veins.
• Bulliform cells are large, void cells which are responsible for the curling of leaves for minimal loss of water.

Write Dicotyledonous and Monocotyledonous Roots.

Question:

Write Dicotyledonous and Monocotyledonous Roots.

Answer:

Dicot Root

• Dicot plants have the taproot system.
• The outermost layer is called the epidermis. The epidermal cells sometimes project out which appear as the root hairs.
• The epidermis is followed by the multi-layered cortex, loosely made of the parenchyma cells with intercellular spaces.
• The inner layer of the cortex is called endodermis, which is tightly packed by the barrel shaped-cells.
• Endodermis is followed by pericycle, which are a few layers of thick-walled parenchyma cells.
• In dicots, the central pith is not distinct.
• There are two to four xylem and phloem.
• The xylem and phloem are remarked by a layer of parenchymatous cells known as conjunctive tissue.

During secondary growth, the cambium separates the xylem and phloem. Pericycle, vascular bundles and pith fuse to form stele in dicots.

Monocot Root

Monocot roots do not show much difference in the anatomy from that of the dicot roots.

• Monocot plants possess an adventitious root system.
• As in the dicots, the epidermis forms the outermost layer, followed by cortex, pericycle, endodermis, vascular bundles (xylem and phloem) and pith (random order).
• Pith is conspicuous and large.
• The number of xylem in a monocot is six or more.
• Secondary growth is not seen in the monocot plants.

Write Dicotyledonous and Monocotyledonous Stem.

Question: 

Write Dicotyledonous and Monocotyledonous Stem.

Answer

Dicot Stem

The dicotyledonous stem is usually solid. The transverse section of a typical young dicotyledonous stem consists of the following parts:

• The epidermis is the outermost protective layer, which is covered with a thin layer of cuticle.
• Epidermis possesses trichomes and a few stomata.
• Cortex is multi-layered cells sandwiched between epidermis and pericycle.
• The outer layer, hypodermis (collenchymatous cells), the cortical layers (parenchymatous cells) and the inner layer, endodermis together make up the three subzones of the cortex.
• Next to endodermis is the pericycle, which is constituted of semi-lunar patches of sclerenchyma.
• ‘Circled’/ ‘ring’ arrangement of vascular bundles is present only in dicot stem.
• The Vascular bundle is conjoint, open and with endarch protoxylem.
• Pith is evident and is made of parenchymatous cells.

Monocot Stem

Monocot stem is usually hollow with no secondary growth. The anatomy of monocot and dicot stem are similar, however, some notable differences are as follows:

• The hypodermis of the cortex in monocots is made of sclerenchymatous cells.
• Vascular bundles are numerous, but scattered, conjoint and closed, surrounded by the ground tissue.
• Phloem parenchyma is absent.

Write major classes of Biomolecules.

Question:

Write major classes of Biomolecules.

Answer:

There are four major classes of Biomolecules –  Carbohydrates, Proteins, Nucleic acids and Lipids. Each of them is discussed below.

Carbohydrates

Carbohydrates are chemically defined as polyhydroxy aldehydes or ketones or compounds which produce them on hydrolysis. In layman’s terms, we acknowledge carbohydrates as sugars or substances that taste sweet. They are collectively called as saccharides (Greek: sakcharon = sugar). Depending on the number of constituting sugar units obtained upon hydrolysis, they are classified as monosaccharides (1 unit), oligosaccharides (2-10 units) and polysaccharides (more than 10 units). They have multiple functions’ viz. they’re the most abundant dietary source of energy; they are structurally very important for many living organisms as they form a major structural component, e.g. cellulose is an important structural fibre for plants.

Proteins

Proteins are another class of indispensable biomolecules, which make up around 50per cent of the cellular dry weight. Proteins are polymers of amino acids arranged in the form of polypeptide chains. The structure of proteins is classified as primary, secondary, tertiary and quaternary in some cases. These structures are based on the level of complexity of the folding of a polypeptide chain. Proteins play both structural and dynamic roles. Myosin is the protein that allows movement by contraction of muscles. Most enzymes are proteinaceous in nature.

Nucleic Acids

Nucleic acids refer to the genetic material found in the cell that carries all the hereditary information from parents to progeny. There are two types of nucleic acids namely, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The main function of nucleic acid is the transfer of genetic information and synthesis of proteins by processes known as translation and transcription. The monomeric unit of nucleic acids is known as nucleotide and is composed of a nitrogenous base, pentose sugar, and phosphate. The nucleotides are linked by a 3’ and 5’ phosphodiester bond. The nitrogen base attached to the pentose sugar makes the nucleotide distinct. There are 4 major nitrogenous bases found in DNA: adenine, guanine, cytosine, and thymine. In RNA, thymine is replaced by uracil. The DNA structure is described as a double-helix or double-helical structure which is formed by hydrogen bonding between the bases of two antiparallel polynucleotide chains. Overall, the DNA structure looks similar to a twisted ladder.

Lipids

Lipids are organic substances that are insoluble in water, soluble in organic solvents, are related to fatty acids and are utilized by the living cell. They include fats, waxes, sterols, fat-soluble vitamins, mono-, di- or triglycerides, phospholipids, etc. Unlike carbohydrates, proteins, and nucleic acids, lipids are not polymeric molecules. Lipids play a great role in the cellular structure and are the chief source of energy.

Write Difference between Red Blood Cells and White Blood Cells.

Question:

Write Difference between Red Blood Cells and White Blood Cells.

Answer:

Difference between Red Blood Cells and White Blood Cells:

The significant differences between red blood cells and white blood cells are as follows:

RBC – Red Blood Cells	WBC – White Blood Cells
Red blood cells are called Erythrocytes.	White Blood Cells are called Leucocytes or Leukocytes.
RBCs have a bi-concave disc shape	WBCs have an irregular shape.
Size varies from 6 – 8 µm in diameter.	Size varies from 12 – 17 µm in diameter.
The lifespan of RBC is about 120 days.	The lifespan of WBC is around 12-20 days after which they are destroyed in the lymphatic system
Red blood cells do not have a nucleus on maturity.	WBCs are characterized by the presence of a large central nucleus.
Due to the presence of haemoglobin, these cells appear red in colour.	These cells are colourless, as they do not have any pigment.
Only one type of RBC exists.	Different types of WBCs are found in the blood such as neutrophils, B lymphocytes, T lymphocytes, monocytes, basophils, eosinophils.
They help in the transport of respiratory gases to different parts of the human body	They help in producing antibodies to fight against disease-causing microbes.
RBCs are produced in the red bone marrow	These cells are produced in the red bone marrow, lymph nodes, and spleen.
The components of red blood cells are haemoglobin.	The components of white blood cells are antibodies with the presence of MHC (major histocompatibility complex) antigen cell markers.
These cells make up around 36-50% of human blood.	They make up around 1% of the human blood.
RBC count: 5 million/ mm³ of blood.	WBC count: 7000–8000/mm³ of blood.
The process of formation of RBC is known as erythropoiesis.	The process of formation of WBC is known as leukopoiesis.
These cells move between the cardiovascular systems.	These cells move between the cardiovascular and lymphatic systems.
Low count of RBCs results in Anaemia.	Low count of WBCs results in Leukopenia.

Write Features and Significance of Meiosis.

Question:

Write Features and Significance of Meiosis.

Answer:

Features of Meiosis

• It results in the formation of four daughter cells in each cycle of cell division.
• The daughter cells are identical to the mother cell in shape and size but different in chromosome number.
• The daughter cells are haploid.
• Recombination and segregation take place in meiosis.
• The process occurs in the reproductive organs and results in the formation of gametes.
• The process is divided into two types-Meiosis-I reduces the chromosome number to half and is known as reductional division. Meiosis-II is just like the mitotic division.

Significance

1. Meiosis is responsible for the formation of sex cells or gametes that are responsible for sexual reproduction.
2. It activates the genetic information for the development of sex cells and deactivates the sporophytic information.
3. It maintains the constant number of chromosomes by halving the same. This is important because the chromosome number doubles after fertilization.
4. In this process independent assortment of maternal and paternal chromosomes takes place. Thus the chromosomes and the traits controlled by them are reshuffled.
5. The genetic mutation occurs due to irregularities in cell division by meiosis. The mutations that are beneficial are carried on by natural selection.
6. Crossing over produces a new combination of traits and variations.