Lecture 6: Plant Structure & Function

Question 1

Describe the primary cell wall of plants

Answer 1

The primary cell wall of plants is found in all plant types.
It is forms a layer on the outside of the plasma membrane and is secreted by the plasma membrane. It is composed of cellulose and protects the cell while providing some structural support. Because it is made from cellulose, it is flexible and more permeable than the membrane.

Question 2

Describe the secondary cell wall of plants

Answer 2

Only SOME plants have cells with secondary cell walls. This is a second layer that surrounds the cell (closer to the cell), secreted by the plasma membrane after the primary cell wall.
The secondary cell wall provides greater protection and structural support as it is composed of cellulose and the rigid molecule, LIGNIN. Lignin is not flexible or permeable.

Question 3

What is lignin? Which plant cell wall contains it?

Answer 3

Lignin is a molecule that makes woody stems rigid. The secondary cell wall is composed of lignin and cellulose.

Question 4

Describe the plasmodesmata

Answer 4

Plasmodesmata are the small channels lined with plasma membrane between cell walls that connect different cells. The plasmodesmata allows for the movement of cytoplasm that can carry molecules or organelles (like chloroplasts that move in response to light) between different cells.

Question 5

Describe turgor pressure

Answer 5

When the central vacuole of a plant cell fills with water, it expands and exerts a force from the inside of the cell against the primary cell wall. Since the primary cell wall is made of flexible cellulose, the cell expands slightly.

Question 6

Where is water stored inside a plant cell that expands?

Answer 6

Inside the central vacuole

Question 7

T or F: Turgor pressure provides some structural support? Even for some non-vascular plants and herbaceous non-woody plants?

Answer 7

TRUE because the cells are filled and expanded to their maximum they become rigid and structurally supportive. Turgor pressure is the reason moss doesn’t look like seaweed outside of water.

Question 8

What is the opposite of turgid?

Answer 8

Flaccid. When a plant does not have enough water and becomes wilted, the cells are flaccid.

Question 9

What are the 3 tissue systems that plant cells are organized into? Briefly describe each.

Answer 9

1. Dermal tissue system: the external covering of the plant
2. Vascular tissue system: the transport system within plants that moves water, nutrients, and sugars.
3. Ground tissue system: tissues that are neither vascular or dermal. This system functions in storage, photosynthesis, and support.

Question 10

The dermal tissue system is located in the ____? which is the _____ tissue layer in plants?

Answer 10

The dermal tissue system is located in the EPIDERMIS which is the OUTER TISSUE LAYER in plants

Question 11

The epidermis (or dermal tissue system) is composed of which 3 cells? What are their functions?

Answer 11

1. Epidermal cells: produce the WAXY CUTICLE that protects the cell from water loss.
2. Guard cells: are located in shoots to form the stomata that allow for gas exchange. The guard cells control the opening and closing of the stomata.
3. Root hairs: are not actual cells, but are an extension of the epidermal cells. Their main function is to absorb nutrients and water by increasing the surface area of the plant. They also help minimally in structural support.

Question 12

The ground tissue system is composed of which 3 cells?

Answer 12

1. Parenchyma cells
2. Collenchyma cells
3. Sclerenchyma cells

Question 13

Describe the parenchyma cells. Which tissue system do they belong to?

Answer 13

The parenchyma cells are part of the ground tissue system.

They are LIVING, thin, flexible cells that perform MOST METABOLIC FUNCTIONS of the plant (including photosynthesis).

Question 14

Describe the collenchyma cells? Which tissue system do they belong to?

Answer 14

The collenchyma cells are part of the ground tissue system.
They are LIVING cells that have irregularly thickened cell walls to provide some flexible structural support. More so than the parenchyma cells.

Question 15

Describe the sclerenchyma cells? Which tissue system do they belong to? Are they dead or alive at functional maturity, why?

Answer 15

The sclerenchyma cells belong to the ground tissue system.
They are DEAD at functional maturity in order to perform their job more efficiently. They are VERY RIGID cells due to their secondary cell wall that contains lignin to provide STRUCTURAL SUPPORT.
They are dead at maturity because once they have produced their secondary cell wall, the cell wall can perform the functions this cell needs to do (provide structural support).

Question 16

Which of the 3 ground tissue cells has a secondary cell wall? why?

Answer 16

The sclerenchyma cells have a secondary cell wall because their main function is to provide structural support to the plant. the secondary cell wall contains lignin and therefore is extremely rigid.

Question 17

The vascular tissue system is composed of which 2 tissues? Function of each?

Answer 17

1. Xylem tissue transports water and mineral nutrients throughout the plant body.
2. Phloem tissue transports sugars made from photosynthesis around the plant body.

Question 18

The vascular tissue system is composed of which 4 cells? and to which tissue do the cells belong?

Answer 18

Composed of…

Xylem tissue:

• tracheids
• Vessel elements

Phloem tissue:

• sieve tube elements
• companion cells

Question 19

What is the structure and function of tracheid cells? Which tissue and which tissue system do they belong? Alive or dead at maturity? why?

Answer 19

Tracheid cells are located in the xylem tissue of the vascular tissue system.

STRUCTURE: they are long, thin tube-like cells that contain lignified secondary cell walls.

FUNCTION: to move water through the plant body, but they are water tight cells so they contain pits (specific openings) to allow water to move between cells.
They are DEAD at functional maturity so their containments can disintegrate and the tube can become hollow and more efficient at transferring water.

Question 20

What is the structure and function of vessel element cells? To which system and tissue system do they belong? Are they alive or dead at maturity?

Answer 20

Vessel element cells are located in the xylem tissues of the vascular tissue system.

STRUCTURE: they are wider and shorter than tracheid cells and are connected from end to end lengthwise to form long tubes. They have pits and perforations at cell ends to allow water to flow more efficiently.
They are dead at maturity because they have a secondary cell wall, so their inside containments can disintegrate and they can become hollow and more efficient at moving water.

FUNCTION: to transport water throughout the plant

Question 21

T or F: Tracheids are more efficient at transferring water than vessel elements?

Answer 21

FALSE. Vessel elements are more efficient at transferring water through plant bodies because they are wider and have large perforations AND pits, rather than just pits and thin tubes.

Question 22

T or F: Tracheids and vessel elements are both dead at functional maturity?

Answer 22

TRUE to allow for more efficient water transfer through the hollow tubes that are supported by the secondary cell wall they produce.

Question 23

What is the structure and function of the sieve tube element cells? to which tissue and tissue system do they belong? are they alive or dead at maturity?

Answer 23

The sieve tube elements are located in the phloem tissue of the vascular tissue system.

STRUCTURE: They do not have secondary cell walls, a nucleus, ribosomes or a vacuole.

FUNCTION: they connect to one another by their sieve plates (like perforations) to transport sugars (dissolved in water) throughout the body of the plant. Since they are alive at maturity, their perforations are plasmodesmata (functioning plasma membrane between different cells) to transfer the sugars.

Question 24

How do sieve tube elements function if they do not contain a nucleus, ribosomes, or a central vacuole?

Answer 24

They have COMPANION CELLS! that consist of all the organelles needed for life and are connected via plasmodesmata to the sieve tube elements to transfer them the proteins they need for life.

Question 25

What is the structure and function of the companion cells? to which tissue and tissue system do they belong? are they alive or dead at maturity?

Answer 25

Companion cells belong to the phloem tissue of the vascular tissue system.

STRUCTURE: these cells contain all the organelles the sieve tube elements and are connected via plasmodesmata to the sieve tube elements.

FUNCTION: they perform all the functions of life and send the nutrients and proteins they generate through the plasmodesmata to the sieve tube elements in order for them to live.

Question 26

What are the two organ systems in plants? What are the organs that make up these systems?

Answer 26

1. Shoot System: consists of
   - Stems
   - Leaves
   - Sometimes flowers
2. Root System: consists of
   - roots
   - sometimes storage organs like tubers in potatoes

Question 27

What is the structure and function of the stem organs? Which organ system do they belong to?

Answer 27

Stems are organs located in the shoot organ system.

FUNCTION: raise the height of the plant to increase exposure to sunlight on leaves for photosynthesis. Stems also raise reproductive structures like flowers or fruits to improve chances of dispersal.

STRUCTURE: A vertical shoot of a plant that grows in height with alternating nodes where leaves attach. Any horizontal shoots are called branches. the tip of a stem shoot will consist of an apical meristem, where growth occurs.

Question 28

What is the structure and function of the leaf organs? to which organ system do they belong?

Answer 28

Leaves are organs in the shoot organ system of plants.

STRUCTURE: Leaf structures vary between species but generally are a flattened blade, to increase surface area, that are connected to the stem via a stalk and have differing (between monocots and eudicots) vein arrangements.

FUNCTION: Leaves are the main photosynthetic organ of plants

Question 29

What is the structure and function of the root organs? to which organ system do they belong?

Answer 29

Roots are an organ in the root organ system.

STRUCTURE: Begins as a primary root that emerges from an embryo and grows lateral roots from there. This structure can differ between monocots and eudicots

FUNCTION: their main function is to grow below the ground surface and absorb nutrients and water for the plant. They can also store carbohydrates. Also provide anchorage for the plant.

Question 30

What do the veins of a monocot leaf look like? What about eudicots?

Answer 30

Monocot’s leaves have vertical veins that run parallel to one another, whereas eudicot’s leaves have netlike veins.

Question 31

How do monocot roots differ from eudicot roots?

Answer 31

Monocot’s generally have a fibrous root system with no main root, whereas eudicot’s generally have one main root called a taproot that then grows lateral roots.

Question 32

What is the structure and function of flowers? which organ system do they belong to?

Answer 32

Flowers are a reproductive organ in the shoot organ system.

STRUCTURE: flowers can vary in structure (depending on whether eudicot or monocot), but grow from the tips of vertical shoots (not the apical meristems).

FUNCTION: flower’s main function is to produce pollen and reproduce.

Question 33

Describe meristems

Answer 33

Areas of rapid cell division that facilitate growth.

They are undifferentiated and have the potential to become any cell type.

Question 34

T or F: plant growth is indeterminate? why/why not?

Answer 34

TRUE. Indeterminate because the meristems allow for constant cell division and plant’s can continue to grow throughout their lives.

Question 35

Describe primary plant growth. Which structure does it occur through? What does it produce?

Answer 35

Primary plant growth is the rapid cell division that occurs through the APICAL MERISTEMS (concentrated areas) at the tips of plant shoots and roots.
Primary growth is VERTICAL elongation.
Apical meristems produce PRIMARY XYLEM and PRIMARY PHLOEM (primary vascular tissue).

Question 36

T or F: apical meristems are located at the very tips of roots? why/why not?

Answer 36

FALSE.
Apical meristems are located just before the tip of the root so it can be protected from damage as new cells elongate through the soil.

Question 37

T or F: shoot apical meristems are just as protected as root apical meristems?

Answer 37

FALSE.

they do not need to be as protected because new cells are elongating into the air which is not as damaging.

Question 38

How do the cells that apical meristems produce help the roots vs. the shoots grow?

Answer 38

In shoots, the cells divide and specialize and allow the plant to grow vertically and create new leaves.

Whereas, in roots, the cells divide and elongate the end of the root further into the soil.

Question 39

What is secondary growth? Which structure does it occur through? what does it produce?

Answer 39

Secondary growth is the growth in WIDTH/diameter of stems and roots in woody plants.
It occurs through the cell division in the LATERAL MERISTEMS.
The VASCULAR CAMBIUM is the lateral meristem structure that produces SECONDARY XYLEM and SECONDARY PHLOEM (secondary vascular tissues) that increase the diameter of woody stems

Question 40

Describe the vascular cambium. To which kind of growth and meristem does it belong?

Answer 40

The vascular cambium is a lateral meristem that grows between the primary xylem and phloem to facilitate secondary growth by producing secondary xylem and phloem to increase the diameter of woody stems.

Question 41

How do primary and secondary growth relate and differ?

Answer 41

Primary growth occurs in the first year of a plant’s life. This is when the primary xylem and phloem are produced.

Secondary growth begins to occur in the second year of a plant’s life (in woody plants). This is when the vascular cambium will grow between the primary xylem and phloem to push them out towards the edges of the cell. Each year a new layer of secondary xylem and phloem are added, but always more xylem, until the phloem eventually sloughs off (because the xylem cells are lignified).

Question 42

Where are xylem and phloem located in a cell in relation to one another?

Answer 42

Xylem is located more towards the inside and phloem more towards the outside.