Plants

Anatomy, Physiology & Photosynthesis

Plant anatomy

• Aerial portion– absorb light energy

– gas exchange of O2, CO2 & H2O

– stomata (holes)– Structural support

• Terrestrial portion– anchorage

– H2O absorption

– nutrient uptake

Leaf epidermal peel

Leaf cross section

Stomata regulate uptake and release of gases not by pressure but by simple diffusion.

In order to exchange gases stomata must remain open and lose large amounts of water.

Is this a good strategy?

Cohesion and adhesion of water!

Water moves due to a concentration gradient and negative pressure!

Sugars Absent 140,000-210,000Amino acids 200-1,000 900-10,000P 70-80 300-550K 200-800 2,800-4,400Ca 150-200 80-150Mg 30-200 100-400Mn 0.2-6.0 0.9-3.4Zn 1.5-7.0 8-23Cu 0.1-2.5 1.0-5.0B 3.0-6.0 9-11NO3

- 1,500-2,000 Absent

NH4+ 7-60 45-846

Substance Xylem Phloem

Typical Ranges for Components of Xylem and Phloem Saps in Higher Plants

Concentrations (g mL-1)

What is photosynthesis?

• The conversion of electromagnetic energy to chemical energy

• Light photons supply the energy to remove the carbon from carbon dioxide and link them together to form a compound of glucose.

light

6 CO2 + 6 H2O C6H12O6 + 6 O2

Recall I mentioned that you learned 1 of the 2 most important chemical equations, well this is the other!

1st Law of thermodynamics

• Energy can not be created or destroyed; it can only undergo conversion from one form to another

• Therefore photosynthesis does not create energy

Photosynthesis

• Process of converting light energy to chemical energy that is useful for biological systems.

• Almost all energy on this planet uses energy originally derived through the process of photosynthesis.

• The reactants and products of the reaction

The Overall Equation for The Overall Equation for PhotosynthesisPhotosynthesis

Unnumbered Figure 7.1

Lightenergy

Carbondioxide

Water

Photo-synthesis Glucose Oxygen

gas

How plants capture electromagnetic energy

• Plant pigments absorb light energy– chlorophyll a, chlorophyll b, carotenoids

Chlorophyll a

Where are the pigments located within a plant cell?

• chlorophyll within the thylakoid membrane

2H2O + 2ADP +2Pi +2NADP+ O2 + 2ATP + 2NADPH + 2H+

6 CO2 + 6 H2O C6H12O6 + 6 O2

chemical equation for photosynthesis

Light dependent reactions:

light

Energy from 4 photons of light

No CO2 used O2 produced as a waste product

H H+ and NADPH, electrons from H end up in NADPH

NADPH is 2 times greater in energy than ATP

6 CO2 + 6 H2O C6H12O6 + 6 O2

Light independent reactions

6CO2 C6H12O6 + 6 O2 used in other reactions

12NADPH 12 NADP+ and 18 ATP 18ADP + 18Pi

Heat

Energy and 12HHeat

Energy

Light dependent reactions + light independent reactions

6CO2 + 12NADPH +18ATP + 12H2O + 12H+ C6H12O6 + 12NADP+ +18PiH2O + 18ADP

Summary equation again:

Three phases of photosynthesis

• Sunlight energy captured

• Using sunlight energy to synthesize ATP (adenosine triphosphate)

• Using ATP to synthesize organic compounds from carbon dioxide

(fixation of inorganic carbon)

Bottom line: we went from light energy to electrical energy and then from electrical energy to chemical bond energy.

Why a carbohydrate?

• If a plant can produce an energetic molecule, like ATP, why bother synthesizing glucose then later convert it back to ATP? PORTABILITY

• ATP and NADPH are fairly unstable compounds. Imagine trying to send these compounds around without losing energy as they go.

Summary of Photosynthesis

cellular respirationcellular respiration

cellulose starchcellulose starch

other organic compoundsother organic compounds

Respiration vs. Photosynthesis?

• Respiration takes energy stored in the chemical bonds of glucose and converts it to ATP.

• Photosynthesis takes energy from light and converts it into glucose.

Photosynthesis

Respiration:

6 CO2 + 6 H2O C6H12O6 + 6 O2

C6H12O6 + 6O2 6CO2 +6H2O

RespirationPhotosynthesis

C6H12O6+ 6O2

6H2O + 6CO2

Light Energy

Heat Energy

• Identify the main regions of a plant (roots, stems and leaves) identify their main functions, the structures within each region that help them carry out those functions, and the physical factors that affect each.

• Explain how the physical environment, particularly water and light availability, can affect plant growth form.

• Identify the main purpose of photosynthesis.• For both the light dependent and light independent reactions be able to

identify:– The source of energy driving each set of reactions, and where it ends up.– The important molecules needed by each set of reactions.– The products of each set of reactions.

• Explain why glucose is a better way of transporting energy than ATP or NADPH

• Explain the importance of the polarity of water to the process of getting water from the roots to the leaves.

• Explain the importance of the products of photosynthesis to the process of respiration and vice-versa.

• Explain the energetic relationship between photosynthesis and respiration.

You should be able to: