Topic 9.1 Plant Structure and Growth

Question 1

9.1.1 Draw and label plant diagrams to show the distribution of tissues in the stem dicotyledonous plant.

Answer 1

• Vascular bundle
  
  • phloem (outer)
  • cambium (middle)
  • xylem (inner)
• Pith (center)
• Cortex (outer)
• Epidermis

Question 2

9.1.1 Draw and label plan diagrams to show the distribution of tissues in the leaf of a dicotyledonous plant.

Answer 2

• Waxy cuticle (thick at top)
• Upper epidermis
• Palisade mesophyll
• Vascular bundle
  
  • Xylem (upper)
  • Phloem (lower)
• Spongy mesophyll
• Lower epidermis
• Waxy cuticle (thin on bottom)
• Stomata (pores)
• Guard cells (on either side of stomatal pore)

Question 3

9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants.

Answer 3

Number of cotyledons (seed leaves)

• Monocotyledons: 1
• Dicotyledons: 2

Leaf veins

• Monocotyledons: parallel venation
• Dicotyledons: net-like venation pattern

Floral organs

• _​​_Monocotyledons: 3 flower parts or multiples of 3
• Dicotyledons: 4/5 flower parts or multiples of 4/5

Roots

• Monocotyledons: root system usually fibrous (no main root)
• Dicotyledons: root system usually has a taproot (main root)

Stem vascular arrangement

• Monocotyledons: vascular bundles arranged throughout system
• Dicotyledon:s: vascular bundles arranged as a ring in stem

Pollen

• Monocotyledons: pollen grain has 1 opening
• Dicotyledons: pollen grain has 3 openings

Question 4

9.1.3 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues.

Answer 4

Upper epidermis

• distribution: top portion, covered by thick waxy cuticle.
• function: prevents water loss even when heated by sunlight.

Palisade mesophyll

• distribution: upper portion of leaf.
• function: consists of densely packed cylindrical cells with many chloroplasts. It is the main photosynthetic tissue, thus placed at top where light intensity is greatest to maximize photosynthesis.

Spongy mesophyll

• distribution: above lower epidermis
• function: loosely packed rounded cells with few chloroplasts provide continuous channels for gas exchange, thus must be near stomata in lower epidermis

Veins

• distribution: throughout the leaf, occurring close to the middle
• function: consists of vascular tissue, located near middle to be close to all cells and to transport raw materials and products of photosynthesis

Lower epidermis

• distribution: bottom surface of leaf, has thinner waxy cuticle than upper epidermis
• function: positioned so that remaining structures of the leaf are protected and supported

Stomata

• distribution: in lower epidermis
• function: a pore that allows CO₂ for photosynthesis to diffuse in and O₂ to diffuse out; located at bottom where there is least transpiration (b/c less light & lower temp.) near stoma

Question 5

9.1.4 Identify the modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils.

Answer 5

Bulbs

• vertical underground stem structures that consist of enlarged leaf bases for food storage
• e.g. onions

Stem tubers

• horizontally growing underground stem structures that store carbohydrates
• e.g. potatoes

Storage roots

• specialized cells in roots that store large quantities of water and carbohydrates
• e.g. carrots, beets

Tendrils

• curly, narrow outgrowths from leaves that provide aid in support and climbing by coiling around objects (may also be formed from modified stems)
• e.g. pea plants produce tendrils from leaves

Question 6

9.1.5 State that dicotyledonous plants have ______ and _______ meristems

Answer 6

Dicotyledonous plants have apical and lateral meristems.

Question 7

9.1.6 Compare growth due to apical and lateral meristems in dicotyledonous plants.

Answer 7

Apical meristems

• occurs at tips of roots and stems
• vertical growth for photosynthesis and uptake of nutrients and water
• produces primary tissues (new plant) and causes primary growth
• results in herbaceous (relating to herbs), non-woody stems and roots
• non-woody

Lateral meristems

• occurs within the stem and older roots
• growth in thickness caused by cambium to make roots and stems more stable, with more xylem & phloem tissue
• referred to as secondary growth (growth of pre-existing plant)
• most trees and shrubs (woody plants) have active lateral meristems
  
  • vascular cambium (remnant part of apical meristem located between vascular bundles) & cork cambium (true secondary meristem located outside vascular tissue)

Similarities

• both help plants grow longer/taller (thickness provides stability for tall plants)
• both are types of meristem tissue causing cell division

Question 8

9.1.7 Explain the role of auxin in phototropism as an example of the control of plant growth.

Answer 8

• Tropism: growth/movement responses to directional external stimuli; there’s positive (towards stimulus) & negative (away from stimulus)
  
  • Phototropism: directional movement of plants in response to light. Positive photopropism in stems, negative in roots.
• Auxins: plant hormones causing positive phototropism of plant shoots and seedlings
  
  • secretes H⁺ into cell walls → loosening cellulose fibres → allows cell expansion
  • shoot tips detect source of light, produce auxin → auxin moves from lighter side to shadier side → promotes cell growth on one side → shoot grows towards light