Plant Biology: Leaf Structure and Growth

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Questions and Answers

What happens to leaves when they are flaccid due to water stress?

They turn yellow and drop off.

They become wider to absorb more light.

They become thicker to retain moisture.

They curl inwards to minimize water loss. (correct)

What type of growth is primarily concerned with increasing the length of roots and stems?

Tertiary growth

Lateral growth

Secondary growth

Primary growth (correct)

Which meristematic layer is responsible for the secondary growth in dicotyledonous plants?

Cork cambium

Vascular cambium (correct)

Interfascicular cambium

Apical meristem

Where is the vascular cambium located in a young stem?

In patches between xylem and phloem. Signup and view all the answers

Which cambium is specifically found between the primary xylem and primary phloem in dicot stems?

Intrafascicular cambium Signup and view all the answers

What is the role of the cork cambium in plants?

To protect the inner tissues and help in water retention. Signup and view all the answers

What initiates the formation of the interfascicular cambium in dicots?

Cells of medullary rays Signup and view all the answers

What is a distinct feature of the vascular bundles in monocot leaves?

They exhibit parallel venation and near similar sizes. Signup and view all the answers

What is the primary function of the pericycle in plant roots?

Initiate lateral roots and vascular cambium Signup and view all the answers

How does the number of xylem bundles in monocot roots compare to those in dicot roots?

Monocot roots typically have more than six xylem bundles. Signup and view all the answers

What region of the root system is described as small or inconspicuous?

Pith Signup and view all the answers

Which tissue develops a cambium ring between the xylem and phloem during root development?

Vascular cambium Signup and view all the answers

What is the role of conjunctive tissue in the root structure?

Connect and support the xylem and phloem Signup and view all the answers

Which of the following statements is true regarding monocotyledonous roots?

They typically have a well-developed pith. Signup and view all the answers

Which layer of the dicotyledonous stem is primarily responsible for protection?

Epidermis Signup and view all the answers

What does the stele in plant roots consist of?

All tissues on the inner side of the endodermis Signup and view all the answers

What is the primary function of the outer hypodermis in the cortex of a young dicot stem?

Mechanical strength Signup and view all the answers

Which characteristic differentiates the vascular bundles in a dicot stem from those in a monocot stem?

Open vascular bundles Signup and view all the answers

What is the role of the endodermis in the cortex?

Storage of starch Signup and view all the answers

In a monocot stem, what surrounds each vascular bundle?

Sclerenchymatous bundle sheath Signup and view all the answers

Which cells in the cortex of a dicot stem are responsible for storing starch?

Parenchymatous cells Signup and view all the answers

What is a main feature of the medullary rays found in stems?

Consist of parenchymatous cells Signup and view all the answers

What feature of the abaxial epidermis in a dorsiventral leaf is commonly observed?

Bears more stomata Signup and view all the answers

Which type of cells provide mechanical strength to the monocot stem's hypodermis?

Sclerenchyma cells Signup and view all the answers

What type of parenchyma is primarily responsible for photosynthesis in the mesophyll?

Palisade parenchyma Signup and view all the answers

Which characteristic is NOT true for isobilateral leaves compared to dorsiventral leaves?

Mesophyll is differentiated into palisade and spongy parenchyma Signup and view all the answers

What is the function of bulliform cells in isobilateral leaves?

Absorbing excess water Signup and view all the answers

How are the xylem and phloem organized within the vascular bundles?

Xylem and phloem are located on opposite sides Signup and view all the answers

What distinguishes the spongy parenchyma from palisade parenchyma?

Spongy parenchyma has air cavities Signup and view all the answers

Which statement about vascular bundles is correct?

Vascular bundles' size varies according to the size of the leaf's veins Signup and view all the answers

What is a key feature of the mesophyll in dicot leaves?

Mesophyll consists of both palisade and spongy parenchyma Signup and view all the answers

Which of the following is NOT a function of the mesophyll?

Water storage Signup and view all the answers

What are the main functions of plant tissues?

Assimilation of food and mechanical support Signup and view all the answers

Which type of tissue system forms the main bulk of the plant?

Ground tissue system Signup and view all the answers

What constitutes the vascular tissue system in plants?

Xylem and phloem Signup and view all the answers

How does secondary growth occur in dicotyledonous plants?

Through the activity of the vascular cambium Signup and view all the answers

What type of vascular bundles are found in monocot plants?

Scattered and conjoint Signup and view all the answers

Why are xylem and phloem referred to as complex tissues?

They perform multiple functions and are composed of different cell types Signup and view all the answers

What feature is characteristic of the cork cambium?

It generates cork tissues Signup and view all the answers

What can be inferred if a transverse section of a plant reveals scattered vascular bundles without phloem parenchyma?

It indicates a monocot plant Signup and view all the answers

Study Notes

Leaf Structure and Function

Leaves can curl inwards when water stressed to minimize water loss
Monocot leaves have parallel venation with similar sized vascular bundles, except in main veins
Dicot leaves have a reticulate venation with varying vascular bundle sizes

Secondary Growth

Primary growth is the increase in length of roots and stems, driven by the apical meristem
Most dicotyledonous plants exhibit an increase in girth, called secondary growth
Secondary growth is facilitated by two lateral meristems: vascular cambium and cork cambium

Vascular Cambium

Responsible for producing vascular tissues - xylem and phloem
In young stems, it is present in patches but later forms a complete ring
Intrafascicular cambium is present between primary xylem and phloem in dicot stems
Interfascicular cambium forms from medullary rays, connecting intrafascicular cambium
Cells of pericycle, which lies next to endodermis, contribute to lateral root formation and vascular cambium
Pith, which is a central area of parenchyma cells, is generally small or inconspicuous

Monocotyledonous Root

Similar in structure to dicot roots with epidermis, cortex, endodermis, pericycle, vascular bundles and pith
Monocot roots typically have more than six xylem bundles (polyarch)
Pith is large and well developed
No secondary growth occurs

Dicotyledonous Stem

Epidermis is the outermost protective layer
Cortex consists of three sub-zones:
- Hypodermis provides mechanical strength
- Cortical layer contains rounded cells with intercellular spaces
- Endodermis, rich in starch, is the innermost layer
Pericycle forms semi-lunar patches of sclerenchyma
Medullary rays are parenchyma cells between vascular bundles
Vascular bundles are arranged in a ring, a characteristic of dicot stems
Each vascular bundle is conjoint, open, and with endarch protoxylem
Pith is the central portion of the stem, composed of parenchyma cells

Monocotyledonous Stem

Possesses a sclerenchymatous hypodermis
Scattered vascular bundles surrounded by sclerenchymatous bundle sheaths
Large, conspicuous parenchymatous ground tissue
Vascular bundles are conjoint and closed
Peripheral vascular bundles are smaller than central ones
Phloem parenchyma is absent, and water-containing cavities exist

Dorsiventral (Dicotyledonous) Leaf

Has three main parts: epidermis, mesophyll, and vascular system
Adaxial epidermis (upper surface) and abaxial (lower) are both covered by cuticle
Abaxial epidermis generally has more stomata
Mesophyll (photosynthetic tissue) contains palisade and spongy parenchyma
- Palisade parenchyma is elongated and arranged vertically
- Spongy parenchyma is oval or round and loosely arranged
Vascular system includes vascular bundles found in veins and the midrib
Vascular bundles are surrounded by thick-walled bundle sheath cells

Isobilateral (Monocotyledonous) Leaf

Similar to dorsiventral but with stomata present on both surfaces
Mesophyll is not differentiated into palisade and spongy parenchyma
Bulliform cells, large empty cells, are found adaxially along the veins

Tissue Systems and their Functions

Epidermal tissue provides protection, composed of epidermal cells, stomata, and appendages
Ground tissue is the bulk of the plant, including cortex, pericycle, and pith
Vascular tissue is composed of xylem and phloem, conducting water, minerals, and food

Differences between Monocots and Dicots

Monocots differ from dicots in vascular bundle type, number, and location
Most dicot roots and stems undergo secondary growth, increasing girth
Wood is secondary xylem, varying in types based on composition and production

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Description

Explore the fascinating world of plant biology, focusing on leaf structure and the processes of primary and secondary growth. This quiz covers leaf venation patterns, the role of vascular cambium, and the morphological changes in dicots. Test your knowledge on how plants adapt to their environment and grow in size.