Biology 3 Marks Question

Tissue System	Tissues present
Epidermal tissue system.	Epidermis, trichomes, hairs, stomata.
Ground tissue system.	Parenchyma, collenchyma, sclerenchyma, mesophyll.
Vascular tissue system.	Xylem, phloem, cambium.

Vascular bundles in dicot stem are arranged in a ring whereas in monocot stem vascular bundles are scattered throughout the ground tissue. On the basis of arrangement of vascular bundles it can be ascertained whether the young stem is dicot or monocot. Besides undifferentiated ground tissue, sclerenchymatous hypodermis, oval or circular vascular bundles with Y shaped xylem are other differentiating features of monocot stem.

Phelloderm, phellogen and phellem together constitute the periderm. Periderm is protective in function. Dicot stems produce cork cambium or phellogen in the outer cortical cells. Phellogen cells divide on both the outer side as well as the inner side to form secondary tissues. The secondary tissue produced on the inner side of the phellogen is called secondary cortex or phelloderm. On the outer side phellogen produces cork or phellem.

When secondary growth occurs in the dicot stem and root, the epidermal layer gets broken. There is a need to replace the outer epidermal cells for providing protection to the stem and root from infections. Therefore, the cork cambium develops from the cortical region. It is also known as phellogen and is composed of thin-walled rectangular cells. It cuts off cells toward both sides. The cells on the outer side get differentiated into the cork or phellem, while the cells on the inside give rise to the secondary cortex or phelloderm. The cork is impervious to water, but allows gaseous exchange through the lenticels. Phellogen, phellem, and phelloderm together constitute the periderm.

	Spring Wood	Autumn Wood
1	The wood formed during favourable growth season (spring and summer), is called spring wood.	The wood formed during unfavourable growth periods (winter and autumn), is called autumn wood.
2	The cambium is very active and the secondary xylem vessels are larger in dimension.	The cambium is less active and the wood produced has vessels of narrow dimension.
3	It is lighter in colour.	It is darker in colour.
4	It has a lower density.	It has a higher density.

1. A particular teacher is responsible for teaching a particular subject in school.

Explanation:
Specialization means expertise in a particular field or a particular task. A person cannot do everything. Someone may have basic idea about most of the things, but the person can be an expert in some selected things only. Let us take the example of a biology teacher. The biology teacher must be having good knowledge of other science subjects; like physics and chemistry but her expertise is biology. She may be able to clear some confusions of a student in physics and chemistry, but when it comes to biology; she can be the best person to give conceptual learning.

1. Collenchyma.
2. Since the endodermal cells are rich in starch grains, it is referred to as starch sheath.
3.  

• The vascular bundle is referred to as 'open'; because it possesses cambium that has the ability to produce secondary xylem and secondary phloem tissues, i.e. secondary growth.
• The vascular bundle is referred to as 'conjoint' because the xylem and phloem are situated along the same radius in the vascular bundle.

The portion of conjunctive parenchyma or tissue present below the phloem bundles dedifferentiates to form brick-shaped cells of vascular cambium. The process of dedifferentiation of conjunctive parenchyma spreads laterally between xylem and phloem bundles. The portion of the pericycle in contact with protoxylem also becomes meristematic. It produces a complete continuous wavy ring of vascular cambium that passes from below the phloem bundles to above the xylem bundles.

(a)Pericycle is located just inner to the endodermis. (b)The protoxylem elements are towards the outer surface, while the metaxylem elements are found towards the centre/ pith.(c)Xylem is exarch.
(d)Parenchyma cells constitute the cortex.

Debark means removal of bark. In common language and economic botany all dead cells lying outside phellogen are collectively called bark [In anatomical usage, bark includes all tissues outside vascular cambium. It is then differentiated into outer bark or rhytidome (consisting of dead cells) and inner bark (or living cells, i.e. periderm and secondary phloem)]. The outer layers of the bark are constantly peeled off on account of formation of new secondary vascular tissues in the interior.

1. An isobilateral leaf shows parallel venation, where the veins except the main/mid vein are of same thickness; as the size of vascular bundles depends on the thickness of the veins, they are near similar in size.
2. Heart wood is dark brown in colour due to accumulation of organic compounds like tannin, resin, oils, gums, and aromatic substances.
3. Cells of phellem are suberised; hence, are impervious to water.
4. The cambium is more active on its inner surface than the outer surface; hence, more secondary xylem than secondary phloem is produced.
5. Phellogen differentiates from the outer layers of cortex during secondary growth; hence, it is a secondary meristem.

Hardwood is the name of dicot wood. The wood contains vessels and is therefore called porous wood. The content of the tracheids is very low (less than 5%). Wood or xylem fibers are abundant. The wood is comparatively difficult to work with. Softwood is the name of gymnospermous wood. This wood is devoid of vessels therefore, also called non- porous wood. The content of tracheids can be 90-95%. Wood or xylem fibers are fewer and the wood is easy to work with.

Yes, Pinus trees are evergreen, coniferous resinous trees. The leaves in gymnosperms are well-adapted to withstand extremes of temperature, humidity and wind. In conifers, the needle-like leaves reduce the surface area. Their thick cuticle and sunken stomata also help to reduce water loss. Unlike deciduous plants, Pinus do not shed their leaves so it is an evergreen tree.

Structure of Monocotyledonous Seed:

1. Generally, monocotyledonous seeds are endospermic but some as in orchids are non-endospermic.

2. In the seeds of cereals such as maize the seed coat is membranous and generally fused with the fruit wall.
3. The endosperm is bulky and stores food. The outer covering of endosperm separates the embryo by a proteinous layer called aleurone layer.
4. The embryo is small and situated in a groove at one end of the endosperm. It consists of one large and shield shaped cotyledon known as scutellum and a short axis with a plumule and a radicle.
5. The plumule and radicle are enclosed in sheaths which are called coleoptile and coleorhiza respectively.

1. The vascular bundles are scattered in the ground tissue. Protoxylem is towards the inner side and meta xylem is towards the outside; there is a protoxylem lacuna just beneath the protoxylem element.
2. Xylem is endarch.
3. Cambium is lacking.

In dicots, cambium is present between phloem and xylem. These types of vascular bundles are capable to form secondary xylem and phloem tissues. These are known as open vascular bundles. In monocots, vascular bundle have no cambium present hence, they do not form secondary tissues. These are known as closed vascular tissues.

Protoxylem	Metaxylem
It is the first or earlier formed xylem. Matures before the growth and differentiation of plant organs. Protoxylem elements are smaller in diameter. Tyioses absent in protoxylem vessels. Fibres are absent.	It is the later formed xylem. Matures after the growth and differentiation of plant organs. Metaxylemd elements are broader and greater in diameter. Tyioses are generally present. Fibres may be present.

2. Instead of wasting our energy on trivial matters, we should focus on more E productive works.

Explanantion:
Focus is very important in life. As a student, we should focus on our study goals and on our career goals. The age of an eleventh class student is the age where foundation of a good future is laid. If someone develops many distractions and indulges in small pleasures of life, he may lose focus from his study and his career goal. Instead, if someone keeps a focus on study and career goal; the future is easily taken care of. Once this phase is over, it would never come back and we cannot undo the wrongs which were done in the past.

1. Heartwood: It is secondary xylem with highly lignified walls. In old trees, considerable region of secondary xylem is dark brown due to accumulation of tannin, resins, oils, gums and other organic materials. The substances make is heart and resistant to microbes and insects.
2. Sapwood: Sapwood is the peripheral region of secondary xylem which is lighter in colour and involved in conduction of water and minerals from root to leaf.

1. It occurs in some arborescent monocots (e.g., Dracaena, Yucca, Agave) and storage roots (e.g., beet, sweet potato).
2. In arborescent monocot stems, a secondary cambium grows in hypodermal region. It later forms conjunctive tissue and patches of meristematic cells. The meristematic patches grow into secondary vascular bundles. Anomalous vascular bundles also occur in cortex (e.g., Nyctanthes) and pith (e.g., Boerhavia). In storage roots (e.g., beet), accessory cambial rings appear on the outside of endodermis. They produce less secondary xylem, but more secondary phloem.

1. The vascular bundles are scattered in the ground tissue. Protoxylem is towards the inner side and meta xylem is towards the outside; there is a protoxylem lacuna just beneath the protoxylem element.
2. Xylem is endarch.
3. Cambium is lacking.

Regions of the Root:

1. Root Cap: The root is covered at the apex by a thimble-like structure called the root cap. It protects the tender apex of the root as it makes its way through the soil.
2. Region of Elongation: A few millimetres above the root cap is the region of meristematic activity. The cells of this region are very small, thin-walled and with dense protoplasm. They divide repeatedly. The cells proximal to this region undergo rapid elongation and enlargement and are responsible for the growth of the root in length. This region is called the region of elongation.

3. Region of Maturation: The cells of the elongation zone gradually differentiate and mature. Hence, this zone, proximal to region of elongation, is called the region of maturation. From this region some of the epidermal cells form very fine and delicate, thread-like structures called root hairs. These root hairs absorb water and minerals from the soil.

• The secondary growth in dicot roots starts with the appearance of cambium in the stelar region.
• The cambium originates from the cells located below the phloem groups and the pericycle cells lying opposite to the xylem groups.
• Initially it is a complete and continuous wavy ring, but later becomes circular in outline.
• The cells of cambium produce secondary xylem elements on its interior and secondary phloem on its outer side.
• A cork cambium originates from the peripheral layers of cortex and it produces secondary cortex on its inner side and cork on its outer side.

Intra fascicular Cambium	Intre fascicular Cambium
Cambium present in between the primary xylem and primary phloem is called-intra fascicular cambium, as in dicot stems.	The cambium present in between the two vascular bundles making the cambium continuous and forming a complete ring of cambium is called interfascicularconbium.

	Heart Wood	Sap Wood
1	It is the central core of wood formed after a certain years of secondary growth.	It is the peripheral part of the wood, formed after certain years of secondary growth.
2	It is composed of dead cells and darker in colour.	It is composed of living cells and lighter in colour.
3	It has no function in conduction.	It helps in conduction.
4	As it contains extractives (gums, resins, tannins, etc), it is more durable and resistant to attack by microbes and insects.	As it does not have these extractives, it is less durable and resistant to attack by insects and microbes.

Stela	Vascular Bundle
Stele refers to conducting tissue or the central part of root or stem in plants. It comprises of vascul tissue, ground tissue and pith and limiting boundaries, i.e., endodermis and pericycle.	Vascular bundle comprises of vascular/ conducting tissues xylem and phloem. Sometimes cambium is also included as in dicots.

	Xylem tracheids	Xylem vessel
1	They are elongated, tube-like, thick-walled (lignified) cells.	They are long tube-like structures formed of a number of vessel members.
2	They have tapering ends.	They have perforated end walls.

The complex permanent tissues are made of more than one type of cells. They are of two types:

1. Xylem.
2. Phloem.

The characteristic features of collenchymatous tissues are listed below,

1. It is present only in layer below the epidermis in dicotyledonous plants.
2. It is found either as a homogeneous layer or in patches.
3. Collenchyma consists of cells which are much thickened at the corners due to a deposition of cellulose, hemicellulose and pectin.
4. The cells may be oval, spherical or polygonal and often contain chloroplasts.
5. These cells assimilate food, when they contain chloroplasts.

Symmetry of Flowers:

1. Actinomorphic (radial symmetry): When a flower can be divided into two equal radial halves in any radial plane passing through the centre, it is said to be actinomorphic, e.g., mustard, datura, chilli.
2. Zygomorphic (bilateral symmetry): When it can be divided into two similar halves only in one particular vertical plane, it is zygomorphic, e.g., pea, gulmohur, bean, Cassia.
3. Asymmetric: (irregular) if it cannot be divided into two similar halves by any vertical plane passing through the centre, as in canna.

Bark is the all tissues exterior to the vascular cambium including secondary phloem and periderm. Bark is of two types. The bark that is formed early in the season is called early or soft bark, while towards the end of the season late or hard bark is formed.

Collenchyma It's function is to provide mechanical support to young growing herbaceous stem. It's cells have angular thickening at corners.

In the transverse section of the stem, the springwood and autumnwood appear in the form of distinct concentric circles known as annual rings. One spring wood circle and one autumnwood circle together constitute an annual ring. Like this, year after year such rings appear and their identity is well-marked.

Functions of major parts of a flowering plant:

• Root: Absorption of water and minerals, anchorage, food storage and hormone & synthesis.
• Stem: Mechanical support and base for aerial parts, conduction of water, minerals and food.
• Leaf: Photosynthesis, food storage.
• Flower: Sexual Reproduction.

Fruit: Storage of seed and nutrients for seed.

Debark means the removal of bark, i.e., all tissue exterior to the vascular cambium, including secondary phloem. Bark refers to a number of tissue types, viz., periderm (phellogen, pheltem and phelloderm) and secondary phloem.

Inter fascicular Cambium its function is to bring about secondary growth in the dicot stem and root. It is a kind of secondary meristematic tissue present in between two vascular bundles.

1. The endodermis is single-layered, made up of barrel-shaped cells which do not enclose intercellular spaces.
2. The young endodermal cells possess an internal strip of suberin and lignin which is known as casparian strips.
3. Endodermal cells lying opposite to the protoxylem groups, remain in the primary stage with usual casparian strips. These unthickened cells are called passage cells. The passage cells are meant for the conduction of fluids inwardly from the cortex and outwardly from the interior to the cortex.
4. Archana was responsible and intelligent student. She was careful for her studies and career.

1. These rings are known as annual ring.
2.  

• The activity of cambium is influenced by internal factors as well as external factors.
• In spring season, the cambium is active and produces large number of xylary elements, with larger diameter; the wood formed in spring, is called early wood or spring wood.
• In winter, the cambium is less active and produces few xylary elements, that too with narrow vessels; the wood formed in winter, is called late wood or autumn wood.
• These two types of wood appear as alternate concentric rings and constitute the annual rings.

3. The age of a tree can be calculated by counting the number of annual rings.

The hormones secreted by plant body influence anatomical changes in it. In the future area of abscission, a special narrow abscission zone develops. It consists of a upper lignified and suberised protective layer. The separation layer consists of unthickened cells where the hydrolysing enzymes develop. Pectinases are secreted out to dissolve middle lamellae. Cellulases bring about hydrolysis of cell walls. Due to this, the separation layer becomes soft and weak. This leads to shedding of leaves from plants.