Plant systems and photosynthesis

Question 1

leaves

Answer 1

main photosynthetic organ; leaves intercept light, exchange gases, dissipate heat and defend themselves from pathogens

Question 2

stems

Answer 2

organ bearing leaves and buds, it elongates and orients the shoot in a way that maximizes photosynthesis by leaves and elevates reproductive structures, facilitating dispersal of pollen

Question 3

nodes

Answer 3

where leaves are attached

Question 4

internodes

Answer 4

stem segments between nodes

Question 5

apical bud

Answer 5

growing shoot tip, where the growth is concentrated

Question 6

axillary bud

Answer 6

can form a thorn or flower

Question 7

roots

Answer 7

anchor the plant and absorb water and minerals

Question 8

dermal tissue

Answer 8

• epidermis
• in woody plants - periderm

Question 9

guard cells

Answer 9

involved in gas exchage

Question 10

trichomes

Answer 10

reduce water loss and reflect excess light

Question 11

cuticle

Answer 11

in leaves and most stems, a waxy epidermal coating that helps prevent water loss

Question 12

vascular tissue

Answer 12

STELE (pillar)

Question 13

xylem

Answer 13

conducts water and dissolved minerals upward (roots to shoots)

Question 14

phloem

Answer 14

transports sugars (products of photosynthesis) from where they’re made to where they’re needed or stored

Question 15

ground tissue

Answer 15

• internal to vascular - PITH
• external to vascular - CORTEX

Question 16

photosynthetic cells

Answer 16

packed with chloroplasts that convert sunlight into chemical energy

Question 17

tube-shaped cells

Answer 17

transport resources (water, minerals, sugar)

Question 18

cells with root hairs

Answer 18

near the tips of roots increase the surface area for absorbing water and minerals

Question 19

taproot

Answer 19

one main, vertical root

Question 20

mycorrhizal associations

Answer 20

symbiotic interactions with soil fungus to increase absorption

Question 21

photosynthesis

Answer 21

the conversion process that transforms the energy of sunlight into chemical energy stored in sugars and other organic molecules

The light reactions in the thylakoid membranes split water, releasing O2, producing ATP and forming NADPH.
The Calvin cycle in the stroma forms sugar from CO2, using ATP for energy and NADPH for reducing power.

Question 22

chloroplast

Answer 22

eukaryotic organelle that absorbs energy from sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water

• mainly found in MESOPHYLL (interior of leaf)
• microscopic pores - STOMATA
• has 2 membranes surrounding a dense fluid - STROMA
• suspended within the stroma is a third membrane system, made up of sacs - THYLAKOIDS
• CHLOROPHYLL - pigment - resides there

Question 23

light reactions

Answer 23

solar energy into chemical energy; produces both NADPH which is the source of electrons and ATP which is the versatile energy current of cells - no sugar!; light-dependent

Question 24

light reactions - step 1

Answer 24

Energy from light excites an electron (e–) from chlorophyll, which is transferred to the primary electron acceptor in photosystem II.

Question 25

light reactions - step 2

Answer 25

2. In the thylakoid space, water is split into:
   
   1. 2 e–, which replace chlorophyll’s electron twice,
   2. 2 H+, which contribute to the high [H+] in the thylakoid space, and
   3. an O atom, which joins another O, forming O2 gas.

Question 26

light reactions - step 3

Answer 26

As electrons travel down the electron + transport chain, 4 H are pumped into the thylakoid space, increasing [H+], decreasing the pH.

Question 27

light reactions - step 4

Answer 27

In chemiosmosis, the diffusion of H+ from the thylakoid space back to the stroma down the [H+] gradient powers ATP synthase, producing ATP.

Question 28

light reactions - step 5

Answer 28

5. Low-energy e– from water end up in NADPH (high-energy e–).
   
   1. NADPH formation removes H+ from the stroma, decreasing its [H+], increasing the pH.

Question 29

Calvin cycle

Answer 29

uses the chemical energy of ATP and NADPH to reduce CO2 to sugar; light-independent, as it doesn’t require light directly

Question 30

Calvin cycle - step 1 - carbon fixation

Answer 30

1. The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to
   a five-carbon sugar named ribulose bisphosphate (which is abbreviated RuBP).
2. The enzyme that catalyzes this first step is RuBP carboxylase-oxygenase, or rubisco (This is the most abundant protein in chloroplasts and is also thought to be the most abundant protein on Earth.)
3. The product of the reaction is a six-carbon intermediate that is short-lived because it is so energetically unstable that it immediately splits in half, forming two molecules of 3-phosphoglycerate (for each CO2 fixed).

Question 31

Calvin cycle - step 2 - reduction

Answer 31

1. Each molecule of 3-phosphoglycerate receives an additional phosphate group from ATP, becoming 1,3-bisphosphoglycerate.
2. Next, a pair of electrons donated from NADPH reduces 1,3-bisphosphoglycerate, which also loses a phosphate group in the process, becoming glyceraldehyde 3-phosphate (G3P).
3. Specifically, the electrons from NADPH reduce a carboxyl group on 1,3-bisphosphoglycerate to the aldehyde group of G3P, which stores more potential energy. G3P is a sugar - the same three-carbon sugar formed in glycolysis by the splitting of glucose.
4. For every three molecules of CO2 that enter the cycle, there are six molecules of G3P formed. But only one molecule of this three-carbon sugar can be counted as a net gain of
   carbohydrate because the rest are required to complete the cycle.
5. The cycle began with 15 carbons’ worth of carbohydrate in the form of three molecules of the five-carbon sugar RuBP.
6. Now there are 18 carbons’ worth of carbohydrate in the form of six molecules of G3P.
7. One molecule exits the cycle to be used by the plant cell, but the other five molecules must be recycled to regenerate the three molecules of RuBP.

Question 32

Calvin cycle - step 3 - regeneration of the CO2 acceptor (RuBP)

Answer 32

1. In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle into three molecules of RuBP.
2. To accomplish this, the cycle spends three more molecules of ATP.
3. The RuBP is now prepared to receive CO2 again, and the cycle continues.
   One molecule of G3P exits the cycle per three CO2 molecules fixed and is converted to glucose and other organic molecules.

Question 33

light spectrum

Answer 33

• Light is a form of electromagnetic energy.
• The colors we see as visible light include those wavelengths that drive photosynthesis.
• A pigment absorbs light of specific wavelengths; chlorophyll a is the main photosynthetic pigment in plants.
• Other accessory pigments absorb different wavelengths of light and pass the energy on to chlorophyll a.
• A pigment goes from a ground state to an excited state when a photon of light boosts one of the pigment’s electrons to a higher-energy orbital. This excited state is unstable.
• Electrons from isolated pigments tend to fall back to the ground state, giving off heat and/or light.
• A photo system is composed of a reaction-center complex surrounded by light-harvesting complexes that funnel the energy of photons to the reaction-center complex.
• When a special pair of reaction-center chlorophyll a molecules absorbs energy, one of its electrons is boosted to a higher energy level and transferred to the primary electron acceptor.
• Photosystem II contains P680 chlorophyll a molecules in the reaction-center complex; photosystem I contains P700 molecules.
• Linear electron flow during the light reactions uses both photosystems and produces NADPH, ATP, and oxygen.
• Cyclic electron flow employs only one photosystem, producing ATP but no NADPH or O2.
• During chemiosmosis in both mitochondria and chloroplasts, electron transport chains generate an H+ gradient across a membrane.
• ATP synthase uses this proton-motive force to make ATP.

Question 34

photosystems

Answer 34

composed of a reaction-centre complex surrounded by several light-harvesting complex

Question 35

light-harvesting complex

Answer 35

consists of various pigment molecules (which may include chlorophyll a, chlorophyll b, and multiple carotenoids) bound to proteins; the number and variety of pigment molecules enable a photosystem to harvest light over a larger surface area and a larger portion of the spectrum than could any single pigment molecule alone

Question 36

primary electron acceptor

Answer 36

a molecule capable of accepting electrons and becoming reduced

Question 37

linear electron flow

Answer 37

light drives the synthesis of ATP and NADPH by energizing the two types of photosystems embedded in the thylakoid membranes of chloroplasts - the key to this energy transformation is a flow of electrons through the photosystems and other molecular components built into the thylakoid membrane

Question 38

carbon cycle

Answer 38

part of the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth