ALE #4 BOT 101
Name______________________________
1. When a young oak was 5 m tall, a thoughtless person carved his initials in its
trunk at a height of 1.5 m above the ground. Today the tree is 10 m tall. How
high above the ground are those initials? Explain your answer in terms of the
manner of plant growth.
1.5 m. The tree grows in height from the shoot apical meristem at the top of the tree, so
the carved initials will essentially stay at the same height.
2. Explain why pruning certain types of fruit trees increases future fruit harvest.
For a tree to produce a fruit, vegetative apical meristems must be converted into
determinate, floral meristems. Pruning a tree suppresses apical dominance, causing
more axillary buds to become active. The more axillary meristems that become
active, the more opportunities for flower (and thus fruit) production.
3. List and describe the 5 types of specialized types of plant cells and describe how
their structures are adapted for their specific functions.
Cell type
Parenchyma
Collenchyma
Function
photosynthesis
provide support to
“young” areas of a
plant (immature
vascular system)
Schlerenchyma structural support
Xylem cells:
water transport
tracheids &
vessel
elements
Phloem cells:
sugar transport
sieve-tube
members &
companion
cells
Structure
high concentration of chloroplasts
unevenly thickened primary cell walls, no
secondary walls. This provides flexible support
without restraining the growth of the plant.
Thick secondary walls, dead at maturity
both cells are more or less arranged end to end,
with pits allowing for water transport. Dead at
maturity – this offers less resistance to water flow.
sieve tube cells are chains of cells arranged end-toend, with holes at the ends for sugar flow. These
cells lack a nucleus, ribosomes, and vacuole. This
offers less resistance to sugar flow. For each sieve
tube cell there is a companion cells next to it,
which helps load sugars into the sieve tube cell.
The companion cell does have a nucleus and
ribosomes, which may also serve the sieve tube
cell. Since sugars provide fuel for cellular
respiration, and they need to be shipped to specific
parts of the plant, these cells remain alive at
functional maturity.
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4. How does primary growth differ from secondary growth?
Primary growth involves growth in height, due to elongation of cells produced by
apical meristems. Secondary growth only occurs in woody species (trees &
shrubs), and involves growth in girth (circumference). It occurs when the
vascular cambium produces secondary xylem and secondary phloem, and the cork
cambium produces the periderm.
5. What are the three types of plant tissues and the functions of each?
Dermal tissue – protection, secretion of the waxy cuticle in shoots, leaves; root hairs for
absorption in roots
Ground tissue – photosynthesis, storage (for starch, cellulose), and structural support
Vascular tissue – xylem for transporting water & nutrients, phloem for transporting the
sugars made by photosynthesis.
6. What are the principal functions of roots? Describe several modified roots and
their functions
Roots anchor the plant to the earth, and they absorb water and nutrients. Prop roots
provide structural support to the lower part of the shoots of some “top-heavy” plants like
maize. Storage roots (ex. sweet potato) store carbohydrates and essential nutrients below
ground until the plant is ready to use those resources for flowering/fruiting. Strangler
roots strangle and eventually kill nearby plants – competitive advantage! Buttress roots
provide structural support to some very tall trees. Pneumatophores grow up out of
swampy areas to obtain oxygen for cellular respiration.
7. Describe several modified leaves, and how their shape reflects environmental
adaptations
Tendrils – rope-like leaves that can wrap around anything nearby. Allows the plant to
grow vertically and laterally without much energy devoted to the girth and support of the
plant stem. Especially useful for plants growing along fences or areas with a dense
understory of shrubs.
Cactus spines – sharp, pointed projections perpendicular to the vertical stem. The sharp
point prevents herbivores from eating the stem to obtain water. Spines can also reflect
UV light away from the stem. The spines generally are non-photosynthetic – this is better
left to the stem, since it is indirectly exposed to the intense desert sun.
Some succulents do have very thick, fleshy leaves that are modified to hold large
amounts of water. This helps the plant maintain photosynthesis during periods of
drought.
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8. From plants and people (p 100): what are the 3 main types of plant textile fibers?
Describe the difference between each, and give one example of each
1. Bast fibers (a.k.a soft fibers) – ex. Flax and hemp. These fibers are derived from
the stem of the plant. These are typically spun into thread for use in fabrics.
2. Leaf fibers (a.k.a hard fibers) – These are derived from the leaves of the plant, and
are used more in rope making than in fabrics. Ex. Manila hemp and sisal
3. Surface fibers – these fibers are derived from accessory structures of the seeds or
fruits. Cotton is a great example!
9. From plants and people: page 117: List several root crops, and identify the 2 most
important root crops world-wide. What is a biennial?
The two most important root crops worldwide are cassava (manioc) and sweet
potatoes. Other examples include: carrots, beets, parsnips, rutabagas, and
radishes.
A biennial is a plant that completes its life cycle in two growing seasons. During
the first season, it only produces vegetative growth – no flowers or fruits. During
this time it stores starches below ground, typically in a tap root, to be used the
following spring for new growth. During the second growing season, the plant
will produce flowers and fruits, and then die.
10. From plants and people page 140: Define lumber, pulp, plywood, and fiberboard.
Lumber: square-edged boards that are cut from logs. They are cut into standard widths
and heights
Pulp: This is paper “slush.” Conifer wood is ground up, mixed with chemicals, and then
pressed into giant rolls of paper.
Plywood: These are thin sheets of wood, sliced from a log, and then glued together
Fiberboard: This is a formed by pressing the wood pulp slush into a board
11. What is the difference between a hardwood and a softwood (p.140)?
A softwood is another name for a conifer, and a hardwood is another name for flowering
trees.
12. From plants and people page 145: what are the 3 main causes of tropical
deforestation?
subsistence agriculture, commercial logging, and cattle ranching
13. From Plants and people page 161: Why are leaves so sensitive to air pollution?
This is because the stomata are on the leaves – the stomata are holes where the
leaf takes in carbon dioxide, but there is nothing to prevent the plant from taking
in all the other gasses and pollutants that may be in the air. There are no, or very
few, stomata on the stems, and none on the roots.
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