Plant Biology: Leaf Anatomy and Functions

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Questions and Answers

What happens to guard cells when they take in water?

They remain unchanged.

They become turgid and open the stomata. (correct)

They become flaccid and close the stomata.

They deflate and prevent water loss.

Which vascular structure is responsible for transporting water and minerals?

Bundle sheath

Phloem

Xylem (correct)

Mesophyll

What provides structural support to the leaf?

Veins (vascular bundles) (correct)

Phloem

Xylem

Epidermis

Which of the following describes the bundle sheath?

It is made of thicker-walled parenchyma cells. Signup and view all the answers

In dicots, how do the veins in leaves typically behave?

They create a network with various directions. Signup and view all the answers

What type of cells do guard cells originate from?

Epidermis cells Signup and view all the answers

What is the main role of phloem in plants?

Distributing sugars and carbohydrates Signup and view all the answers

How are the veins in monocots typically characterized?

They are parallel and lack differentiation. Signup and view all the answers

What type of placentation is characterized by the placenta forming along the ventral suture?

Marginal Placentation Signup and view all the answers

Which of the following is an example of a plant that exhibits epigynous flowers?

Apple Signup and view all the answers

What is the main purpose of the embryo in a seed?

To develop into a new plant Signup and view all the answers

Which characteristic defines free central placentation?

Ovules attached to a central axis Signup and view all the answers

What type of pollination occurs when pollen from a flower fertilizes its own stigma?

Self-Pollination Signup and view all the answers

Which of the following plants is an example of a multiparous or polychasial arrangement?

Calotropis Signup and view all the answers

Basal placentation is characterized by which of the following?

A single ovule arising from the base of the ovary Signup and view all the answers

What is a unique structure found in some seeds, specifically in plants like fig?

Hypanthodium Signup and view all the answers

What is the definition of endosperm in the context of seeds?

Nutritive tissue that supports the embryo Signup and view all the answers

Which floral part is located above the gynaecium in epigynous flowers?

Calyx Signup and view all the answers

Which process describes the transfer of pollen grains from the anther to the stigma?

Pollination Signup and view all the answers

What are cotyledons and their significance in seeds?

They determine whether the plant is a monocot or dicot Signup and view all the answers

Which type of seed retains its endosperm during germination?

Endospermic (albuminous) seeds Signup and view all the answers

What type of arrangement is present in a polycarpellary syncarpous ovary?

Central axis with attached ovules Signup and view all the answers

Which of the following is an example of a non endospermic seed?

Sunflower Signup and view all the answers

What structure in a seed develops into the root?

Radicle Signup and view all the answers

What is cleistogamy?

Flowers that remain closed and enable self-pollination Signup and view all the answers

Which of the following describes a raceme?

Long peduncle with stalked flowers arranged acropetally Signup and view all the answers

What is the primary mode of pollination facilitated by insects called?

Entomophily Signup and view all the answers

In which type of flower arrangement are the flowers arranged centripetally?

Umbel Signup and view all the answers

What kind of pollination is achieved by wind?

Anemophily Signup and view all the answers

Which example is characteristic of a spadix?

Banana Signup and view all the answers

Which flower type has sessile flowers and resembles a raceme?

Spike Signup and view all the answers

What is hydrophily?

Pollination through water Signup and view all the answers

What is the primary location of photosynthesis in plants?

Mesophyll layer of leaves Signup and view all the answers

Which of the following is produced as a waste product of photosynthesis?

Oxygen (O₂) Signup and view all the answers

During which reactions is chlorophyll involved in absorbing sunlight?

Light-Dependent Reactions Signup and view all the answers

What do the light-independent reactions use to convert carbon dioxide into sugars?

ATP and NADPH Signup and view all the answers

What is the primary function of stomata in plants?

Gas exchange Signup and view all the answers

Which part of the chloroplast contains thylakoids where light-dependent reactions occur?

Thylakoid membranes Signup and view all the answers

What does Glyceraldehyde-3-phosphate (GA3P) convert into?

Glucose and sucrose Signup and view all the answers

What ensures the activation of certain enzymes in the Calvin Cycle?

Light presence Signup and view all the answers

Study Notes

Guard Cells and Stomata

Guard cells control the opening and closing of stomata.
Guard cells change shape due to water movement.
Turgid guard cells open stomata, allowing for gas exchange.
Deflated guard cells close stomata, minimizing water loss.
Guard cells contain chloroplasts, unlike most epidermal cells.

Vascular Bundles in Leaves

Veins, or vascular bundles, are scattered throughout the leaf mesophyll.
Xylem transports water and minerals from roots to leaves.
Phloem distributes sugars and carbohydrates produced during photosynthesis.
Bundle sheath surrounds vascular tissue and is made of thicker-walled parenchyma cells.

Leaf Skeleton

Veins provide structural support to the leaf.
Veins run in various directions, especially in dicots.
Vein networks facilitate efficient transport.

Monocot Leaf Structure

Monocots typically have parallel veins.
Monocots lack differentiation between palisade and spongy mesophyll layers.

Epigynous Flowers (Inferior Ovary)

Thalamus is fused with the ovary, placing calyx, corolla, and stamens above the gynaecium.
Ovary is inferior, meaning it is located below other floral parts.
Examples: Sunflower, Cucumber, Apple.

Free Central Placentation

Found in polycarpellary syncarpous ovaries that are unilocular.
Ovules are attached to a central axis and not connected to the ovary wall.
Examples: Dianthus (carnation), Saponaria, Portulaca.

Basal Placentation

Characteristic of polycarpellary and unilocular ovaries.
Only one ovule is present and arises from the base of the ovary.
Example: Sunflower.

Pollination

Transfer of pollen grains from the anther to the stigma.

Self-Pollination (Autogamy)

Pollen from a flower's anther fertilizes its own stigma.
Homogamy: Anthers and stigmas mature simultaneously.
Cleistogamy: Flowers do not open, facilitating self-pollination without external agents.

Cross-Pollination (Allogamy)

Pollen is transferred from the anther of one flower to the stigma of another.
Facilitated by various agents: insects, wind, water, animals.

Types of Inflorescence

Racemose or Indefinite Inflorescence
- Peduncle continues to grow, producing flowers acropetally (younger flowers at the top).
- Examples:
  - Raceme: Long peduncle with stalked flowers arranged acropetally (e.g., Mustard, Radish).
  - Spike: Similar to raceme but with sessile flowers (e.g., Rangoon creeper).
  - Spadix: Short peduncle with numerous small unisexual flowers covered by a boat-shaped bract called spathe (e.g., Banana, Arum).
  - Catkin: Spike with unisexual sessile flowers on a long peduncle (e.g., Mulberry, Oak).
  - Umbel: Shortened axis with flowers having equal stalks arranged centripetally (e.g., Coriander, Cumin).
  - Spikelet: Characteristic of Gramineae family, small, branched spikes with bracts (e.g., Ixora, Jasmine).
Cymose or Definite Inflorescence
- Peduncle ends in a flower, and new flowers are produced laterally.
- Examples:
  - Solitary Cyme: Single terminal flower (e.g., Hibiscus).
  - Biparous or Dichasial: Main axis terminates in a flower, then two axillary flowers develop (e.g., Jasmine).
  - Multiparous or Polychasial: Main axis ends in a flower with several laterally produced flowers (e.g., Nerium, Calotropis).
Special Types:
- Include unique structures like: hypanthodium (e.g., peepal, fig), verticillasters (e.g., sacred basil, mentha), and cymose-umbel (e.g., onion).

Seed Morphology

Seeds are fertilized ovules and crucial for plant reproduction.
Seed Components:
- Endosperm: Nutritive tissue supporting the embryo.
  - Endospermic (Albuminous) Seeds: Endosperm remains during germination and is partially absorbed by the embryo (e.g., wheat, rice).
  - Non-Endospermic (Exalbuminous) Seeds: Endosperm is fully absorbed by the embryo during development (e.g., sunflower, tamarind).
- Embryo: Develops into a new plant.
  - Contains an apical meristem (plumule - shoot development), radicle (root development), and cotyledons (seed leaves, determining monocot or dicot).

Photosynthesis Structures

Mesophyll: Middle layer of leaf cells where photosynthesis occurs.
Stomata: Small openings on the underside of leaves for gas exchange (CO₂ in, O₂ out).
Chloroplasts: Organelles where photosynthesis happens in autotrophic eukaryotes.
- Double Membrane Envelope: Outer and inner membranes.
- Thylakoids: Disc-shaped structures stacked within the chloroplast.

Photosynthesis Steps

Light-Dependent Reactions:
- Location: Thylakoid membranes of chloroplasts.
- Process: Chlorophyll absorbs sunlight, converting it into chemical energy.
- Inputs: Water (H₂O).
- Outputs: Oxygen (O₂), ATP, and NADPH.
Light-Independent Reactions (Calvin Cycle):
- Location: Stroma of chloroplasts.
- Functions: Utilize ATP and NADPH from light-dependent reactions to convert carbon dioxide (CO₂) into sugar molecules.
- Does not directly use light but relies on products from the light-dependent reactions.
- Enzymes involved are activated by light.
Products:
- Glyceraldehyde-3-phosphate (GA3P): A simple carbohydrate that can be further converted into sugars (glucose, sucrose).
- Oxygen (O₂): Released as a waste product.

Chemiosmosis

Proton Flow: The proton gradient generated during the electron transport chain generates potential energy.

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Description

This quiz covers the anatomy and functions of leaf structures, including guard cells and stomata, vascular bundles, and leaf skeletons. It also distinguishes between monocot and dicot leaf structures. Test your knowledge on these fundamental plant biology topics!