10th Science Unit 12 Plant Anatomy and Plant Physiology Book Back Answers

Endodermis is the innermost layer of the cortex; its cells are barrel-shaped and show band-like thickenings of suberin on radial and inner tangential walls.

These thickenings are the casparian strips.

Endarch means protoxylem lies towards the centre and metaxylem towards the periphery.

This arrangement is seen in the stem, while roots are exarch.

When xylem and phloem lie on the same radius, the bundle is called conjoint.

In radial bundles they lie on different radii, alternating with each other.

Anaerobic respiration takes place without oxygen; glucose is converted into ethanol (ethanol fermentation by yeast) or lactic acid.

$C_6H_{12}O_6 \rightarrow 2CO_2 + 2C_2H_5OH + \text{Energy (ATP)}$, so ethyl alcohol is formed.

Krebs cycle (TCA cycle) occurs in the mitochondrial matrix, which contains the enzymes for this cycle.

The electron transport chain, in contrast, is located on the inner mitochondrial membrane.

In the light reaction, water is split (photolysis) in the thylakoid membranes.

Oxygen is released as a byproduct of this splitting of water.

In both dicot and monocot roots, the cortex is a multilayered zone of parenchyma.

Its innermost single layer has barrel-shaped cells with casparian strips and passage cells — this layer is the endodermis.

When xylem and phloem lie on different radii, alternating with each other, the bundle is radial.

Radial vascular bundles are seen in roots.

Glycolysis is the splitting of one glucose (6C) into two pyruvic acid (3C) molecules.

This first step of both aerobic and anaerobic respiration occurs in the cytoplasm of the cell.

In the light reaction, light energy splits water in the thylakoid membranes.

The oxygen released as a byproduct of photosynthesis comes from this splitting of water.

Mitochondria are the main organelles of cellular respiration and produce large numbers of ATP molecules.

Hence they are called the power house of the cell or ATP factory of the cell.

Xylem conducts water and minerals to different parts of the plant.

Phloem conducts food materials (prepared food) to different parts of the plant.

Cuticle is present on the outer wall of the epidermis.

It is a waxy covering that checks evaporation of water and protects the plant.

In monocot stem the vascular bundles are conjoint, collateral, endarch and closed.

'Closed' means cambium is absent between xylem and phloem; cambium is present only in dicot stem (open bundles).

Palisade parenchyma is a part of the mesophyll of a dicot leaf, not of a root.

In the dicot leaf, palisade parenchyma lies just below the upper epidermis and has many chloroplasts for photosynthesis.

Mesophyll is the tissue between the upper and lower epidermis of the leaf.

Its palisade and spongy parenchyma cells contain chloroplasts with chlorophyll, so photosynthesis takes place here.

In aerobic respiration glucose is completely oxidised through glycolysis, Krebs cycle and electron transport chain, giving a large number of ATP molecules.

In anaerobic respiration glucose is only partly broken down into ethanol or lactic acid, so very little ATP is released.

Amphicribral – concentric bundle in which phloem completely surrounds xylem, e.g. Fern.

Cambium – the meristem present in open vascular bundles that brings about secondary growth.

Amphivasal – concentric bundle in which xylem completely surrounds phloem, e.g. Dracaena.

Xylem – vascular tissue that conducts water and minerals to different parts of the plant.

Phloem – vascular tissue that conducts (translocates) food materials to different parts of the plant.

A collateral bundle is a type of conjoint vascular bundle in which xylem and phloem lie on the same radius.

Xylem lies towards the centre and phloem lies towards the periphery.

If cambium is present between them it is open (e.g. dicot stem); if cambium is absent it is closed (e.g. monocot stem).

Photosynthesis uses carbon dioxide taken from the atmosphere.

This $CO_2$ combines with water in presence of sunlight and chlorophyll to form carbohydrates.

In the Calvin cycle (dark reaction) this atmospheric $CO_2$ is reduced into carbohydrates.

Glycolysis is the splitting of one glucose molecule (6 carbon) into two molecules of pyruvic acid (3 carbon).

It takes place in the cytoplasm of the cell.

It is the first step of both aerobic and anaerobic respiration.

Anaerobic respiration takes place without oxygen.

In yeast, glucose is broken down into ethanol and carbon dioxide with release of energy: $C_6H_{12}O_6 \rightarrow 2CO_2 + 2C_2H_5OH + ATP$.

This process is called ethanol (alcoholic) fermentation.

In dicot stem (sunflower) the vascular bundles are conjoint (xylem and phloem on the same radius), collateral (xylem inner, phloem outer), endarch (protoxylem towards centre, metaxylem towards periphery) and open (cambium present between xylem and phloem).

They are limited in number, uniform in size and arranged in the form of a ring around the pith.

A patch of hard sclerenchyma lying outside the phloem of each bundle is called the bundle cap.

Since cambium is present, secondary growth takes place in dicot stem. Xylem conducts water and minerals; phloem conducts food.

Mesophyll is the ground tissue present between the upper and lower epidermis of a leaf; its cells contain chloroplasts.

In a dicot (dorsiventral) leaf the mesophyll is differentiated into palisade parenchyma and spongy parenchyma.

Palisade parenchyma lies just below the upper epidermis; cells are elongated, rich in chloroplasts, without intercellular spaces, and carry out photosynthesis.

Spongy parenchyma lies below the palisade; cells are spherical or oval, irregularly arranged with intercellular spaces and help in gaseous exchange.

In a monocot (isobilateral) leaf the mesophyll is not differentiated into palisade and spongy tissue; cells are irregularly arranged with intercellular spaces.

Sachs (1875) classified the tissue system of flowering plants into three types.

Dermal or epidermal tissue system – epidermis, stomata, epidermal outgrowths; gives protection and prevents water loss.

Ground tissue system – cortex, endodermis, pericycle and pith; stores food, carries out photosynthesis and gives support.

Vascular tissue system – xylem and phloem; transports water, minerals and food.

Photosynthesis (photo = light; synthesis = to build) is the process by which autotrophs like green plants, algae and chlorophyll-containing bacteria use sunlight energy to make their own food.

Carbon dioxide combines with water in the presence of sunlight and chlorophyll to form carbohydrates, and oxygen is released as a by-product.

In the cell it occurs inside the chloroplast: the light reaction in the thylakoid membranes (grana) and the dark reaction (Calvin cycle) in the stroma.

In the plant it occurs in all green parts, especially in green leaves.

Respiratory quotient (R.Q.) is the ratio of the volume of carbon dioxide liberated to the volume of oxygen consumed during respiration.

It is expressed as $R.Q. = \dfrac{\text{Volume of } CO_2 \text{ liberated}}{\text{Volume of } O_2 \text{ consumed}}$.

It has no unit, as it is a ratio of two volumes.

The light dependent reaction (Hill reaction) takes place in the thylakoid membranes (grana) where pigments absorb light energy and convert it into chemical energy as ATP and $NADPH+H^+$.

These products move out of the thylakoid into the stroma.

The light independent reaction (Calvin cycle) in the stroma reduces $CO_2$ into carbohydrates using this ATP and $NADPH+H^+$.

So the assimilatory power (ATP and $NADPH+H^+$) must be made first; without it the dark reaction cannot fix and reduce $CO_2$.

Photosynthesis needs carbon dioxide and water, with sunlight and chlorophyll as essentials.

The balanced reaction is: $6CO_2 + 12H_2O \xrightarrow[\text{chlorophyll}]{\text{Light}} C_6H_{12}O_6 + 6O_2 \uparrow + 6H_2O$

That is, Carbon dioxide + Water $\rightarrow$ Glucose + Oxygen + Water.

Oxygen is released as a by-product, coming from the splitting of water.

The entire process of photosynthesis takes place inside the chloroplast, but the two phases occur at different sites within the organelle.

Light dependent reaction (Hill reaction): It occurs in the thylakoid membranes, i.e. in the grana of the chloroplast, where the photosynthetic pigments are present to absorb light.

Here light energy is converted into chemical energy in the form of $ATP$ and $NADPH+H^+$.

Calvin cycle (dark reaction / biosynthetic phase): It occurs in the stroma, the matrix present inside the chloroplast membranes.

In the stroma the $ATP$ and $NADPH+H^+$ that move out from the thylakoid are used to reduce $CO_2$ into carbohydrates.