Matric Notes Biology Class 9th Ch 4 Cells and Tissues Extra Short & Long Questions

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Short Questions

Q.1) Who proposed the cell theory and what are the main points of the cell theory?

Answer: Cell theory:

1838, a German botanist Mathias Schleiden claimed that all plants were made up of cells. This was supported by a German zoologist, Theodor Schwann, in 1839 who proved that animals were also made of cells. Thus, Schleiden and Schwann proposed that all living organisms are made of cells and presented cell theory. It was the first statement of the cell theory.

 After the first observations of life under the microscope, it took two centuries of research to formulate the ‘cell theory’.

Main points of cell theory:

  Schwann and Schleiden summarized their observations into three conclusions about cells:

• All animals and plants are made up of cells and cell products. Some organisms are unicellular and some are multicellular.
• Cells are the structural and functional units of living organisms.
• New cells arise from the pre-existing cells by cell division.
  

Q.2) Differentiate between simple and compound tissues.

Answer:

Differences between Simple and Compound tissues:

Simple tissues	Compound tissues
They are composed of only one type of cells performing a common function	They are composed of more than one kind of cells and type of cells perform a common function
These type of tissues usually cover the surface of external and internal organs	They are found in the vascular bundles
Simple tissues are mainly concerned with growth and variety of functions	Compound tissues mainly involved in the process of conduction in plants
The cells are packed tightly together.	They are scattered throughout the body.
Example:     Epidermal (in plants) tissues	Example:    Xylem and phloem

Q.3) How cell membrane helps in maintaining equilibrium while exchanging materials with the environment?

Answer: Cell membrane separates the cell content from their external environment. Cell membrane is a selectively permeable membrane which selectively allows the movement of molecules across it. So it controls the movement of materials between cell and environment.

  It also enables the cell to form separate compartments within the cell in which specialized metabolic processes such as photosynthesis and aerobic respiration can take place. Membranes also act as receptor site for the attachment of hormones, neurotransmitters and other chemicals. Thus, it controls the movement of materials passing through it. It allows only the passage of water and other small molecules such as gases and other small molecules such as glucose, amino acids, fatty acids, glycerol, and ions can diffuse slowly through them. So, maintaining equilibrium by this membrane while exchanging material is actually its innate property.

Q.4) Differentiate between endocytosis and exocytosis.

Answer:

Endocytosis	Exocytosis
Endocytosis is a process that brings macromolecules, large particles, and even small cells into the cell.	Exocytosis is the process by which materials packaged in vesicles are excreted from a cell.
In endocytosis, the cell membrane invaginates (folds inward) and takes in the materials from the environment, forming a small vesicle	The initial event in this process is the binding of the vesicle membrane with the cell membrane.
The vesicle separates from the plasma membrane and migrates with its contents to the cell’s interior.	The contents of the vesicle are released into the environment and the vesicle membrane is incorporated into the cell membrane.
Example: Engulfment of bacteria by the white blood cells during defense mechanism	Example: The release of hormones out of the cell

Q.5) How does turgor pressure develop in a plant cell?

Answer: Process of turgor pressure development:

  When a cell is surrounded by water or hypotonic solution, the water moves into the cell vacuole by osmosis. The vacuole increases in size and pushes the cell contents against the cell wall. This pressure which is exerted by the cytoplasm against the cell wall is known as turgor pressure and the phenomena is called turgidity. In turgid condition, the plant cell does not burst because the cell wall is strong and relatively inelastic.

Long Questions

Q.1) Root hairs are adapted to absorptions and xylem to support. Relate their functions to their structure.

Answer: Adaptation of root hairs to their function:

  The function of root hairs is to collect water and mineral nutrients present in the soil and take this solution up through the roots to the rest of the plant. To perform this function the root hair cells have specific adaptations.

• Root hairs are long and narrow in their shape that increases their surface area to absorb water and minerals efficiently.
• The cell sap of root hair has higher salt concentration than surrounding water to absorb water through its movement along the gradient.

Adaptations of xylem tissues to their function:

  The main purpose of the xylem is to transport water and minerals up the stem, from the roots to the leaves. In order for a xylem to carry out its functions successfully and efficiently, the xylem cells have specific adaptations.

• Xylem tissues support the overall structure of the plants because of the presence of two types of cells i.e. vessels and tracheids.
• Vessels cells are short, wide and have thick secondary cell walls. These cells are dead and hollow and join together to form long tubes.
• Tracheids are long, slender cells with overlapping ends. Water move upwards from tracheids to tracheids.
• Xylem tissue is responsible for the transport of water and dissolved substances from roots to upper parts. Due to the presence of lignin in the secondary walls of its cells, xylem tissue also provides support to the plant body.

Q.2) Discuss different types of tissues found in plants. Elaborate your answer with relevant diagrams.

Answer: Plant tissues:

“A plant tissue is a cell or a group of cells  which are structurally and functionally similar and give rise to a large number of cells.”

Types of plant tissue:

Plant tissues are mainly classified into two groups.

I) Simple tissues

II) Compound tissues

I) Simple tissues:Simple tissues are composed of only one type of cells. They are further classified into two main types which are:

i) Meristematic tissues (Embryonic tissues)

ii) Permanent tissues

i) Meristematic tissues (Embryonic tissues):

Meristematic tissues (Embryonic tissues) are made up of those cells which have the ability to divide and produce new cells at the growing points of a plant. The cells of meristematic tissue have dense cytoplasm, a large central nucleus with small or no vacuoles. Cells are alike, with no intercellular spaces and have thin walls.

Types of meristematic tissues:

Meristematic tissues are of two types:

a) Apical meristem:

Apical meristem is present at the apex of root and shoot. Here the cells of meristem divide and re-divide and result in the elongation of stem and root. Such a growth is called primary growth.

b) Lateral meristem:

Lateral meristem is present on the lateral sides of roots and shoot. Here, the cells divide and result in the increase of the thickness of root and shoot. Such a growth is called secondary growth.

ii) Permanent tissues:

The cells of these tissues lack the ability to divide. They originate from the primary meristem. The permanent tissues consist of epidermal, ground, supporting or mechanical tissues.

a) Epidermal tissues:

These tissues are present as the outermost protective covering of leaf, stem, and roots. Cells of the epidermal tissues are flattened and irregular in shape. They are thickly walled and are closely packed with no intercellular spaces. In the stem, the walls of these cells are covered with a waxy material which prevents loss of water. In leaves, the epidermal tissue has small guarded openings called stomata, for gaseous exchange.

b) Ground tissues:

This tissue is present in all parts of the plant except the epidermal tissue and vascular tissue. It is composed of thin-walled cells called parenchyma cells. These cells are oval, spherical or polygonal in shape. Their walls are thin and they store food. In leaves, the ground tissue contains chlorophyll and is called mesophyll tissue which prepares food.

c) Supporting and mechanical tissues:

Plants need support to maintain their shape and remain stable. Supporting tissues provide strength and flexibility to the plant. These are of two types.

• Collenchyma tissue is found in young stems where it provides strength to different parts of the plant.  The cells of this tissue are living, elongated, and polygonal with tapering ends.
• Parenchyma tissues are thick walled dead cells. Walls of these cells are heavily filled with lignin which provides hardness and strength to the cell.

II) Compound tissues:

These are the tissues which are composed of more than one type of cells, performing a common function.  Xylem and phloem tissue is found in the vascular bundles are examples of compound tissues.

i) Xylem tissues

ii) Phloem tissues

i) Xylem tissues:

Xylem tissue consists of two types of cells i.e. vessels and tracheids.

• Vessel cells are short and wide and have thick secondary cell walls. These cells are dead and hollow and join together to form long tubes.
• Tracheids are long, slender cells with overlapping ends. Water moves upward from tracheid to tracheid.
• Xylem tissue is responsible for the transport of water and dissolved substances from roots to the upper parts. Due to the presence of lignin in the secondary walls of its cells, xylem tissue also provides support to the plant body.

b) Phloem tissue:

Phloem tissue consists of sieve tube cells and companion cells.

• In sieve tube cells, protoplasm has no nucleus and the end walls have small pores called sieve plates. The transport of food occurs through the cytoplasm of the sieve tube cells.
• Companion cells accompany the sieve tube cells. They regulate the movement of food through sieve tubes.

Q.3) Describe the nervous, muscular and epithelial tissues.

Answer: 

1) Epithelial tissues:

The interior of the body is physically separated from the outside world by the skin. The skin is made of epithelial tissue, which is in the form of continuous sheets of cells. Epithelial tissue also lines the gut, lungs and urinary tract. Structurally these cells are flattened and elongated.

2) Muscular tissue:

Muscular tissues consist of highly specialized contractile cells or fibers held together by connective tissue. Each muscle fiber is an elongated cell which has the ability to contract and relax.

Types of muscular tissues:

Skeletal, smooth and cardiac muscles are the examples of these tissues.

i) Skeletal muscles:

Skeletal muscles are attached to cartilages and bones with the help of connective tissues called tendons. They are composed of striated (striped) cells that are long and cylindrical. The cells of skeletal muscles contain many nuclei. Skeletal muscles are voluntary and produce powerful, rapid contractions. It helps arms and legs to move.

ii) Smooth muscles:

These are found in the walls of hollow structures such as blood vessels, gut etc. They produce slow contractions. Their contraction moves substances (foodstuff, urine) in the hollow organs. They are composed of spindle-shaped, un-striated muscles and are involuntary in action.

iii) Cardiac muscle:

Cardiac tissues are found in heart. These are composed of branched fibers and are capable of sustained contraction. Their contraction produces heartbeat that propels blood into vessels. They are also involuntary in action.

3) Nervous tissue:

Nervous tissue is composed of nerve cells which are called neurons. Neurons are capable of transmitting nerve impulses to conduct messages in the whole body. Nervous tissues are found in the brain, spinal cord, and nerves.

Q.4) Write a note on the structures of the cell wall, cell membrane, mitochondria, and chloroplast of a plant cell.

Answer: I- Cell wall:

      Cell wall is present in all bacteria, plants, fungi, and some protists. It is located outside the plasma membrane. It provides shape, strength, protection, and support to the inner living matter (protoplasm) of a cell. The thickness of the cell wall varies from cell to cell.

Primary cell wall:

  The outer layer of the plant cell wall is known as the primary wall. It is made of cellulose.

Secondary cell wall:

   Some plant cells also have secondary walls on the inner side of the primary wall. It contains cellulose, lignin, and other chemicals.

  An electron microscope reveals that in the primary and secondary cell wall, the cellulose fibers are present in a crisscross manner which provides rigidity.

Cell wall structure of different organisms:

• The cell wall of Prokaryotes is composed of peptidoglycan (Murein). It is a single large molecule made of amino acids and sugar.
• The cell wall of fungi is made of chitin.
• The cell walls of protists are made of a variety of chemicals.

II- Cell membrane:

       Cell membrane or plasma membrane is present in all cells and is the outermost layer of protoplasm. It is the outermost layer of the animal cell. In the cells of bacteria, plants, fungi, and some protists, cell membrane lies beneath the cell wall.

Fluid Mosaic Model of cell membrane:

  Different models have been presented to understand the structure of cell membrane. Singer and Nicolson proposed “Fluid Mosaic Model” which is the most acceptable model. According to this model, cell membrane consists of a lipid bilayer in which protein molecules float while some stay embedded in the bilayer. Carbohydrate molecules are joined with proteins (in the form of glycoproteins) or with lipids (in the form of glycolipids).

3- Mitochondria:

      In prokaryotes, mitochondria are absent and it is thought that energy required is produced in the cytoplasm by anaerobic respiration or by mesosomes.

Mitochondria in eukaryotic cells:

  Mitochondria are found in eukaryotic cells. They are bounded by a double membrane. The outer membrane is smooth. The inner membrane is folded inwards, giving rise to extensions called cristae. Cristae increase the surface area on which respiratory process takes place.

Function of mitochondria:

  Mitochondria are the powerhouse of the cell because they carry out respiration in cell and produce energy in the form of ATP.

4- Chloroplast:

      The most important and abundant plastids are the chloroplasts in plants. These present in green parts of plants, particularly in leaves where photosynthesis takes place. Structure of chloroplast:

   A chloroplast is bounded by a double membrane. The outer membrane is smooth while the inner membrane gives rise to sacs called thylakoids. The stack of thylakoids is known as granum (plural: grana). The thylakoids contain chlorophyll. The semi-fluid present inside chloroplast is called stroma.

 Mitochondria and chloroplasts have their own DNA. Mitochondria also have their own ribosomes, which are similar to the ribosomes of bacteria.