Plant Anatomy Lab Key
Answer these questions for Part 1:
1. List 3 functions for each of the major plant parts; roots, stems and leaves.
Stems – support, transportation, photosynthesis for herbaceous plants
Roots – absorption, anchorage, transport, storage
Leaves – photosynthesis, light absorption, transpiration
2. Where in the root are the cells that have secondary walls located?
In the center.
Answer these Questions for Part 2:
1.
Describe the characteristics of primary and secondary cell walls.
Primary cell walls are composed mostly of cellulose and are somewhat stretchable. They
may be thin and delicate or thick and tough. They are found in living cells that are
actively carrying on metabolic activities. Secondary cell walls are laid down after a cell
matures. The protoplast often dies after depositing the secondary wall, so no further
metabolic activities take place. Secondary walls are strong and rigid and are mostly
found in specialized cells that have a support function. Lignin preserves the secondary
cells walls as well as strengthening them. (ex: wood)
2.
Define the three tissue systems.
Dermal - epidermis
Ground – parenchyma, collenchyma, and sclerenchyma
Vascular – xylem and ploem
Maristematic – primary maristem, cambium and pericycle
3.
Describe the general functions of dermal tissue.
Outer covering that protects and regulates the passage of materials in and out of the plant.
4.
Explain how and why the epidermis of roots and stems differs.
The stem most likely with have cuticle to prevent drying out while the root will not so
that it can absorb waters and minerals.
5.
Explain the function of guard cells.
Guard cells regulate the stomata to control the amount of carbon dioxide that enters and
water from transpiring.
6.
How are the guard cells different from the other epidermal cells?
They contain chloroplasts and are also a different shape.
7.
What is the purpose of root hairs?
To increase surface area for the root.
Answer these questions for Part 3:
1.
Describe the general functions of parenchyma tissue in stems and leaves.
Photosynthesis
2.
Why are the leaf parenchyma cells so loosely packed? (Hint: The spaces between
the parenchyma cells are continuous with the stomata.)
Carbon dioxide can circulate freely among the parenchyma cells via the intracellular
spaces.
3.
Why do root cells require oxygen?
They need it for aerobic respiration, just like the rest of the plant. When soil becomes
packed or water-logged, roots don't get enough oxygen to metabolize.
4.
Why is there no cuticle on the root epidermis?
Because roots must take up water. The cuticle on the stem and leaves keeps water in the
plant; in the root, it would prevent water from entering the plant.
5.
What similarities can you observe between the parenchyma cells in the root cross
section and in the stem cross section?
Parenchyma cells in both cross sections are thin walled and have irregular shapes. In
roots, parenchyma makes up the cortex and may contain stored starch. In stems,
parenchyma is located in the pith.
6.
Describe the general function of collenchyma and sclerenchyma tissue.
To give support and strength to plants.
7.
Collenchyma cells and sclerenchyma fibers are similar in form and function.
What are their differences, and why might these differences be important to a
plant?
Collenchyma cells have a primary cell wall and a living protoplast. Fivers have
secondary cell walls and no protoplast. Therefore collenchyma cells can still metabolize
and grow, while sclerenchyma cells are actually dead. Collenchyma cells are also more
flexible, since they retain the stretchable primary cell wall.
8.
Why do you think you found coilenchyma and sclerenchyma cells in stem and
leaf tissue, but not in the root?
Above-ground plant parts need support, while roots do not.
Answer these Questions for Part 4:
1.
Describe the general function of xylem and list its cell types.
Carry water and minerals up from the roots. Cell types – tracheids and vessel elements
2.
Describe the general function of phloem and list its cell types.
Carry food down from the leaves. Cell types – sieve-tube members and companion cells.
3.
Notice that the vessel elements you have observed are hollow, since the
protoplasts have died, and their cross-sectional area is very large compared to that
of other cells. How are these structural features related to the function of the
xylem?
The vessel elements serve as pipes to conduct water. The larger the diameter of the pipe,
the less resistance it offers to water flow. Similarly, the absence of the protoplast
removes an obstruction.
4.
In the stern, phloem is located exterior to the xylem. Explain why it is then logical
that phloem in the leaf should be located below the xylem.
The leaf grows from the stem. Try to visualize how the vascular tissue of the stem is
continuous with the vascular tissue of the midrib of the leaf.
5.
As the stem gains in girth, the vascular bundles are joined into a continuous ring,
and the width of the band of xylem increases. The band of phloem, however,
remains approximately the same width as old phloem cells are crushed by the new
growth. Explain this difference between xylem and phloem. (Hint: Consider the
cell walls.)
Xylem elements have thick, hard secondary cell walls. The cells of phloem tissue, on the
other hand, have primary cell walls that are easily crushed by the pressure of the
expanding xylem.
Answer these questions for Part 5:
1. Describe the changes in cell size and structure in the stem tip. Begin at the youngest
cells at the apex and continue to the xylem cells.
The size of the cells increases as you move away from the apex. The vascular tissues elongate
and develop interesting cell walls.
2. The meristems of plants continue to grow throughout their lifetime, an example of
indeterminate growth. Imagine a 200-year-old oak tree, with active meristem
producing new buds, leaves, and stems each year. Contrast this with the growth pattern
in humans.
Humans grow to a certain size and age, after which the only growth is for maintenance and
repair, not an increase in size. This is determinate growth.
Answer these questions for Part 6:
1. What has happened to the several years of phloem tissue production?
Phloem gets crushed toward the periderm on the outside of the tree.
2. Based on your observations of the woody stem, does xylem or phloem provide
structural support for trees?
xylem
Part 5: Questions for Review
1. If you are looking at a slide of a thin section of plant tissue, what clues might you
have to tell you whether a cell has a primary or secondary cell wall?
Thickness of the cell wall or differential staining. If the cell has a protoplast (which is often
but not always apparent), it has a primary cell wall.
2. What are the general functions of the following:
Dermal tissue; Regulation of passage, of substances and from the environment, protection
against water loss; mechanical protection.
Vascular tissue: conduction of food and water through the plant (xylem is also a support
tissue).
Ground tissue: Storage; support; photosynthesis.
3. How do the epidermal tissues of roots differ from those of stems and leaves? Suggest
a reason for the differences.
The epidermal tissues of roots have little or no cuticle. In some parts of the root there are also
root hairs. Stems and leaves are covered with a cuticle. The differences are a result of the
different junctions of the organs: Roots absorb water from the giound and need a large
surface area and permeable epidermis; stems ami leaves are above ground and susceptible to
water loss.
4. Figure 4 shows the weight change in three apples over time. Which apple had its
cuticle removed? Explain your answer.
The cuticle was removed from apple b. Once this protective barrier was gone, the fruit lost
weight by dehydration
5. How does the function of the parenchyma located in leaves differ from the function of
the parenchyma located in the roots?
Parenchyma cells in the leaves carry out photosynthesis. Parenchyma cells in the wots store
sugar or starch produced by photosynthesis.
6. Describe how vessel elements are adapted for conducting water. Vessel elements
have large diameters and holes in the walls to lessen resistance to water flow. They
also have thick secondary walls so they can withstand the pressure of the water
(raveling through them.
Location(s)
Primary or
Secondary Wall
Function(s)
Epidermis
Living or
Dead at
Maturity
Living
Primary
Outer layer of
plant
Protection; regulation of
substances entering and
leaving plant
Parenchyma
Living
Primary
Throughout plant
Food storage; photosynthesis
Collenchyma
Living
Primary
Beneath
epidermis, along
midrib
Support
Sclerenchyma Dead (usually)
fibers
Secondary
On outside oj
vascular bundles
Support
Sclereids
Dead (usually)
Secondary
Could be anywhere Support or protection
in plant
Tracheids
Dead
Secondary
Xylcm fin
vascular bundle)
Carry water (also give
support)
Vessel elements Dead
Secondary
Xylem (in
vascular bundle)
Carry water (also give
support)
Conduct food through plant
Sieve -tube
members
Living
Primary
Phloem (in
vascular bundle)
Companion
cells
Living
Primary
Phloem (in vascular Conduct jood through plant
bundle)
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Primary meristems – dividing cells, small, thin walled – gives rise to primary body –
found in stem and root tips.
Vascular cambium – dividing cells, small, thin walled – gives rise to secondary xylem
and phloem – found in stem and root
Pericycle – dividing cells, small, thin walled – gives rise to lateral roots – found in
root
Periderm – compact, prismatic, suberized – water retention – woody stem
Other Main Ideas:
1. Plant tissues arise either from primary growth (growth from the tips of the roots and shoots)
or from secondary growth (an increase in girth).
2. In primary plant growth the epidermis is generally a single layer of cells, although there are
plants that have multiple layers of epidermis. When plants undergo secondary growth, they
develop a more complex dermal layer.
3. If secondary growth occurs in stems, the epidermis will be replace by periderm, which
constitutes part of the bark on trees. Some of the cells in the periderm have secondary cell
walls.
Adaptions of plant cells and structures to the land environment:
Environmental factor
Adaptions to land environment
Desiccation
Cuticle, stomata, gametangia, sporangia
Transport of materials between plant and
Roots that lack cuticle, root hairs present
environment
Gas exchange
Stomata with guard cells
Anchorage in substrate
Fibrous roots, taproots
Transport of materials within plant body
stems (vascular tissue)
Sexual reproduction without water
Pollen grain, ovule, fruit, flowers, endosperm,
seeds, carpel
Dispersal of offspring from immobile parent
Fruit, seeds