Name: ________________________________________ Date: __________________
AP Biology – Continuous Quiz-M - PLANTS
1. Water and minerals in the soil have two ways to enter the roots called the apoplastic
route and the symplastic route. The former describes the solution traveling through the
cell walls, while the later describes the solution moving through the cytosolic of cells and
passing from cell to cell via plasmodesmata. Sometimes the solution can switch from
one route to the other via the transmembrane route. However, in the end, all solutions
must enter the symplastic route when it hits the layer of cells just outside the xylem and
phloem called the endodermis thanks to the impermeable casparian strip in its cell wall.
Therefore the solution MUST cross the cell membrane now and this is what gives the
plant strict control over what enters.
2. Transpiration is the process used by plants to move water and minerals from the soil
upward to the rest of the plant through the xylem, which are dead, hollowed out cells
through which the water moves. Ultimately, the water will leave through the stomates in
the leaves, which are governed by guard cells. The solution moves solely by the process
of diffusion and since we are talking water it is more specifically called osmosis.
Therefore, the water is always moving from a high water potential in the soil to a very
low water potential in the air. The reason it is so low in the air is because the air is
mostly nitrogen and has a very low water concentration. None of this would be possible
without two very important properties of water, namely cohesion (water bonding to
water) and adhesion (water bonding to the inside of xylem cells). This is because as
water evaporates from the leaves it will pull on neighboring water molecules via their
hydrogen bonds, and the same bonds are used to grab the xylem cells to prevent back
flow down the plant. This process is known as the cohesion-tension hypothesis.
3. Describe how guard cells open and close stomates in leaves:
Guard cells will open when there is sunlight and available water to allow
transpiration and gas exchange. They achieve this by pumping potassium (K+)
either into or out of the cell. If they pump K+ in then the water potential of the
cytosol will drop and be less than the extracellular fluid. This will cause water to
diffuse into the cell resulting in turgor pressure and the stomata will open. If K+ is
pumped out of the cell then the extracellular fluid will have the lower water
potential and water will diffuse out and the cells will be flaccid resulting in closed
stomata.
4. Four factors that influence the rate of transpiration in plants are light, humidity, wind, and
temperature. State whether the factor increases or decreases the rate of transpiration and justify
your answer.
Process
Rate
(Increase/Decrease)
Light
Increase
Humidity
(increasing)
Decrease
Wind
Increase
Temperature
(increasing)
Increase
Justification
More light mean more stomata will open and
transpiration will increase up until a saturation point
where opening more beyond this will make no
difference.
As humidity increases the air accepts fewer water
molecules reducing the rate of evaporation from the
leaves.
Wind will move the humid air around the leaves out
of the way and displace it with less humid allowing
for evaporation rates to increase.
The kinetic energy of the water molecules will
increase making diffusion/osmosis and evaporation
(liquid to gas) quicker.
5. Compare mycorrhizae to rhizobium.
Mycorrhizae:
Fungus that grows in association with the roots of plants in a usually mutualistic relationship
where the hyphae of the fungus extend the roots to obtain more water and nutrients while the
plant supplies the fungus with organic materials (food).
Rhizobium:
Genus of nitrogen fixing bacteria that live in the root nodules of legumes (plants with pods like
peas, peanuts, clover, etc…) in a mutualistic relationship. The plants get NH3 from the bacteria
and the bacteria get organics (food) from the plant.
6. Some plants are considered “carnivorous”. They still do photosynthesis like any other plant to
make their food. For what reason are they “carnivorous” then?
They live in soil that is low in particular minerals and the animals (usually insects) contain these
minerals.
7. Define circadian rhythm and give on example in humans and one in plants.
Circadian Rhythm: roughly 24hour cycles in organisms including plants and animals
Humans- hunger, sleep, etc…
Plants- flower opening and closing, leaf
movement, stomatal opening and closing
Name: ________________________________________ Date: __________________
AP Biology – Continuous Quiz-N - PLANTS
1. a) In contrast to transpiration, plants move organic molecules like sucrose up and down
through the phloam cells, which are living unlike xylem cells, using the process of
Translocation. The direction depends on the time of the year. In early spring when leaves
are being made net flow will be upward and in summer when photosynthesis is at its
maximum it will be downward. The mechanism behind this process is known as pressure
flow. The place where the sugar is coming from (either roots or leaves depending on the
time of the year) is known as the sugar source, and the place the sugar is going is known
as the sugar sink.
b) Show how this process works using a labeled figure:
2. Plants, like humans, use a number of different hormones to coordinate their many cells to
work as a single entity. One such class of hormones is called auxin. The specific
naturally occur member of this class is indoleacetic acid (IAA). They are heavily
involved in regulating the growth of shoots (stems) toward light, a process known in
general as phototropism. Since it is growing TOWARD light we more specifically call it
positive phototropism as opposed to growing AWAY from light, which is called negative
phototropism. This is in contrast to say an animal moving (locomoting) toward or away
from light, which is called phototaxis. This hormone class is produced and secreted from
apical meristem located at the tips of growing shoots. The way these hormones cause the
growth toward light is by activating proton pumps, which pump protons out of the cell
causing the pH around the cell wall to decrease in cells on the shaded side of the shoots
only. This weakens the cell wall and causes these cells to get longer, which does not
occur to the cells on the side of the stem being hit with light. The result is that the stem
bends toward the light source. This process was first described by none other than
Charles Darwin (and son) in 1880.
3. Identify three other tropisms and describe each. Include and circle the one that auxin is
also thought to play a role in stimulating:
Tropism
Description
Geotropism
(involves auxin)
Thigmotropism
Growth in response to gravity (roots exhibit positive geotropism)
Hydrotropism
Growth in response to presence of water (roots exhibit positive
hydrotropism)
Growth in response to touch (vines wrapping around objects)
4. Plants can sense light/darkness using cytosolic (location) receptor proteins known as
phytochromes, which contain a light-sensing photoreceptor domain and an enzymatic
kinase domain. The former domain, in order to sense light (which means the domain must
undergo a conformational change when light hits it) has a cofactor called a chromophore
that is able to absorb red (color) light. The receptors exist in two forms, Pr and Pfr, that
can switch back a forth depending on the wavelength of light hitting the protein. In the
dark, the receptors are in the Pfr form, but when hit with red (color) light they switch to
the active Pfr form. The result is signal transduction, which likely involves a
phosphorylation cascade allowing for signal amplification followed by activation of
transcription factors to alter gene expression resulting in cellular responses like plastid
differentiation to chloroplasts. The ratio of the two receptor forms to each other in the
cells allows the plant to determine levels of light through the day and year. These
pathways are no different from the cell signaling pathways we have already seen accept
the “ligand” in this case is light. The same three general stages occur, namely reception,
transduction, and response.
Name: ________________________________________ Date: __________________
AP Biology – Continuous Quiz- O - PLANTS
5. a) Define Photoperiodism
The response of an organism to the length of day or night – the photoperiod is the length
of daylight/darkness in a day. For example an 8:16 photoperiod is 8 hours day and 16
hours night.
b) Compare short day, long day and day-neutral plants
Short-Day
Plants that flower only when nights are longer than an uninterrupted critical period (days
are short).
Long-Day
Plants that flower only when nights are shorter than a particular critical length (days are
long)
Day-Neutral
These plants don’t care…they flower regardless of day length
c) Look at the figure below showing an experiment done on short day plants.
What does this indicate the plants are actually measuring and why?
In this experiment, group one show the plants flowering in an 8:16 photoperiod. Group
two reveal that if the daytime is extended to 16 hours (16:8 photoperiod) then no
flowering occurs. Group three, however, shows that if the plants were measuring day
length then they should have measured 8 hours of day regardless of the night pulse, but
they don’t flower. Therefore, they are likely measuring the length of the dark period.