Stephanie Phillips

BIO 203

Lecture Test #1

February 23rd, 2015

1.) Magnesium is extremely important for plants, especially for photosynthesis. It is a large

molecule and is capable of releasing an electron for the light reaction of photosynthesis.

The chlorophyll contains magnesium, which is the reason it is able to capture light from

the sun. Magnesium captures the usable light from the sun and gives chlorophyll its color

by reflecting the wavelength of light that it cannot use, which happens to be green.

2.) Plants avoid the toxic effects of metabolic waste in a few different ways. One way is to

store their waste in dead spaces. Take for an example, a tree. A tree is like a straw and the

inside is alive but the inside is dead, so it stores waste in the dead, inside area. Also,

oxygen is a waste product of photosynthesis and is disposed of through the plant’s

stomata where the wind will blow it away. However, if the weather conditions are too

calm, oxygen molecules can build up and cause photorespiration. Plants need a little bit

of water, but too much can be detrimental. They can get rid of excess water through

transpiration.

3.) Chemiosmosis occurs in the chloroplast of a plant during photosynthesis. Near the

beginning of the light reaction, photolysis takes place via the oxygen evolving complex

and hydrogen ions, or protons, are released into the lumen where they form a high

concentration proton gradient. Hydrogen ions are also being pumped across the thylakoid

membrane because of the electrons on the electron transport chain. In groups of 3, the

protons travel through an enzyme called ATP synthase. The enzyme acts as a sort of

rotor, and the end product is energy. That energy is then used to help the already existing

ADP and a phosphate group come together and form ATP, which will then go on to the

Calvin cycle.

4.) Unfavorable environmental conditions such as heat, wind, and humidity can increase

water loss through the stomata in several ways. When there is an excessive amount of

heat and light from the sun, water vaporizes almost twice as fast. Wind increases water

loss when a plant’s stoma is open because it is simply blowing the water away. If

conditions are humid, too much water can build up which lowers the plant’s transpiration

rate because the water doesn’t have anywhere to transpire.

5.) Generally, the stoma of a plant is found in the epidermis, on the underside of the plant’s

leaf. In order to do gas exchange, guard cells open and close the stoma. If stomata are

found on a plant, it tells the finder that gas exchange is taking place, which will soon lead

to photosynthesis. Factors such as heat, wind, and humidity influence when the guard

cells open and close their stoma.

6.) Plant cells are different than animal cells in several ways. One of the major differences is

that plants have chloroplasts (a type of plastid) and animals don’t. Other plastids which

store starch and synthesis fatty acids are present in plants but not in animals. Another

difference is in the cell wall. Plants have a cell wall outside of their cell membrane,

whereas animals only have a cytoskeleton outside of their cell membrane. Also, plants

have a central vacuole which takes up approximately 90 percent of the entire cell, but in

animal cells, there can be one or more vacuoles and they comparatively aren’t as big.

Plants also have a cytoplasmic connection called plasmodesmata and animals don’t.

7.) There are a plethora of carbohydrates that play a critically important role in plants.

Cellulose is the most abundant carbohydrate on earth and is a major component of the

plant’s cell wall. Its function is to aid in structure and give the cell strength.

Hemicellulose also serves as a structural polysaccharide that is in the cell wall of a plant.

Amylose and fructose are used for storage. Sucrose is used by the plant as its number one

transporter of sugar. Hydrophilic carbohydrates, such as pectin, serve as a plasticity tool,

helping the plant be flexible so that it doesn’t tear as it is growing. Plants also have

deoxyribose, which is a 5 carbon carbohydrate that is used in DNA. Glucose is also used

by plants for respiration and storage.

8.) There are several similarities as well as several differences between the xylem and

phloem of a plant. For starters, they are both a part of the complex vascular tissue system.

They also both have parenchyma and sclerenchyma cells as part of their mature

conducting tissue. Another similarity is in their shape. Xylem and phloem are both

shaped like tubes, or straws. Xylem and phloem are both found in all plants. One of the

major differences between them is they primary function. The xylem’s function is to

move water and minerals around in the plant. Transpiration occurs in the xylem. The

phloem’s function is to move dissolved solutes, such as sugar, around to different parts of

the plant. Translocation occurs in the phloem. Another major difference is that the cells

that make up the xylem are primarily dead, whereas the cells that make up the phloem are

primarily alive. Another difference is a plant’s xylem has perforation plates, whereas its

phloem has sieve plates. Xylem is unidirectional phloem is bidirectional.

9.) a.) Photorespiration is a process that occurs in plants during hot and dry conditions. As a

survival technique, plants close their stomata to prevent excessive water loss, which

causes a build-up of O2. The O2 gets in the way of CO2 and RubisCo binds with O2 by

accident. It is very detrimental to a plant that cannot perform an alternate form of

photosynthesis such as C4 and CAM photosynthesis.

b.)

C3 C4 CAM

Which group/percent of plants?

All plants. 85% of plants exclusively perform C3

.4% of plants do C4, but it is mostly corn and the grass family

10% of plants do CAM photosynthesis including cacti and pineapple

Environmental conditions? Cool, moist, and normal light

Hot, dry, and during the summer are favorable

Hot and dry

Does photosynthesis occur in one cell or two?

One cell Two cells One cell

Which enzyme is the dominant carbon-fixer,RuBisCo or PEP carboxylase?

RuBisCo PEP carboxylase PEP carboxylase

What time of day do the carbon-fixation reactions occur?s

Daytime Daytime Night time