09. Autotrophs & Energy

Lecture 9

Autotrophy vs Heterotrophy

^^Autotrophy^^ → make their **own complex carbohydrates** for nourishments from **inorganic** carbon sources

^^Heterotrophy^^ → use **organic** sources of **carbon** synthesized by others to derive E (consumer other organisms)

Photosynthesis vs Chemosynthesis

^^Photosynthesis^^ → converts **CO2** to complex sugars → derives energy from **light**

^^Chemosynthesis^^ → converts **CO2** (or methane) to complex sugars → derives energy from **oxidation**

\*similar but diff E sources

What is light?

**Electromagnetic radiation**

Wave-Particle Duality

Radiation behaves as both a **wave** & **particle** (photon = light particle)

Electromagnetic radiation can be described as **wavelength** & **photon E**

Relationship B/w Wavelength & Energy

**Longer** wavelengths → **less** energy

**Shorter** wavelengths → **more** energy

Can have too much & not enough E for photosynthesis

Define: PAR

PAR → __**P**__**hotosynthetically** __**A**__**ctive** __**R**__**adiation**

Consists of visible light → \~400-700nm (purple-red) → can be used to **photosynthesize**

Subject to conditions → ex. shade, water depth, etc.

PAR Availability in a Forest Environment

(3)

**Top** → **more PAR** more light b/c less blocking it

As you go **further down** → **lower** PAR availability

Organisms **adapt** to exposure to **more/less PAR**

PAR in Water:

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\--A-- light abs by autotrophs near surfaces emitting --B--

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\--C-- light abs by autotrophs at great depths emitting --D-- but organisms must be --E-- to use this light range

A → **red**

B → **green**

\
C → **blue**

D → **red** (chlorophyll abs green & blue → reflects red)

E → **adapted**

Three PAR Zones in Aquatic Systems

^^**Eu**photic (sunlight) zone^^ → sunlight penetrates this layer → only zone w **photosynthesis**

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^^**Dys**photic (twilight) zone^^ → sunlight dec rapidly w depth → **no photosynthesis** possible here b/c not enough E for it

\
^^**A**photic (midnight) zone^^ → sunlight does not penetrate at all → zone in **entirely dark**

Photosynthetic Response Curves

Displays **energy limitation** in plants

Photosynthetic rates will **inc.** w inc. light (photon flux density) up **until** a **certain point**

Define: Lsat, Pmax, & LCP

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Determine A, B, & C in terms respiration relative to photosynthesis

^^Lsat^^ → irradiance at saturation → **light saturation point**

^^Pmax^^ → **max net photosynthesis**

^^LCP^^ → light compensation point → light intensity where **photosynthesis = respiration** → if more light is available, produces more sugars than it uses

\
A → respiration < photosynthesis

B → respiration = photosynthesis

C → respiration > photosynthesis

Response Curves Within a Species

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Open vs Shade: Pmax & Lsat

Can depend on location

^^Open^^ → higher Pmax & Lsat

^^Shade^^ → lower Pmax & Lsat (more efficient at using E)

Sun Plants Response Curves

(2)

Achieve **higher Pmax**

but are **inefficient** in using **low PPFD** (fewer photons) → bad dealing w sudden low levels of light

Shade Plants Response Curves

(3)

Achieve only **small Pmax**

but **more efficient** at using **low PPFD** (fewer photons)

**Low Lsat** → can be damage in sunny sites/suddenly exposed to too much light

Higher photosynthetic rates

Basic Chemical Reaction of Photosynthesis

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(+ origin/use of compounds)

^^**6 CO2 + 6 H2O → C6H12O6 + 6 O2**^^

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**CO2** → enter through **stomata** in the leaves (via diffusion)

**H2O** → enter through **water transportation**

**Glucose** → used to **gain E** via respiration

**O2** → a **byproduct** that is essential for many organisms

C3 Photosynthesis:

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Time & Place

**No** anatomic/time **separation** of processes

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^^Initial C fixation^^ → **mesophyll** (day)

^^Calvin cycle^^ → **mesophyll** (day)

C3 Photosynthesis:

Process (2)

**CO2** combines w **RuBP** (5C) catalyzed by **RUBISCO** enzyme

Produces **2 PGA** molecules (3C acids)

Issues w C3 Photosynthesis in Hot Climates

(3)

1. **RUBISCO** is **inefficient** at high temps
2. **Opening stomata** wastes water → **water loss possible** but is the only wat to get CO2 in & O2 out
3. **Closed stomata** → O2 inc. **suppressing photosynthesis**

C4 Photosynthesis:

Time & Place & How Accounts for Heat Dilemma

**Anatomic separation** of processes

Adaption → allows it to **open** stomata **less** often

\
^^Initial C fixation^^ → **mesophyll** (day) → O2 can accumulate here

^^Calvin cycle^^ → **bundle sheath cells** (day) → can keep stoma closed

C4 Photosynthesis:

Process

^^Mesophyll cells^^ → **CO2** combines w **PEP** (3C) catalyzed by **PEP carboxylase** → produces a **4C acid**

4C acids produces in the mesophyll diffuse to bundle sheath

^^Bundle sheath cells^^ → **4C acids** broken down into **3C acid** & **CO2**

Then enters the Calvin cycle (like C3 photosynthesis)

How does C4 Photosynthesis Process Increase Water Efficiency?

(2)

PEP carboxylase → high affinity for CO2 → can **reduce internal [CO2]** to very low → **inc. CO2 gradient** → inc. rate of CO2 diffusion inward → ^^need to open stomata less to get enough CO2^^

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Removing RUBISCO from the high O2 area → can’t bind O2 (b/c in high \[CO2\] area) which leads to release of CO2

Why are there more C3 than C4 Photosynthesis Plants in Edmonton

^^C4 pathway^^ → **more H2O efficient** → not as much of a limiting factor here

^^C3 pathway^^ → **more E efficient** → evolutionarily more advantageous at this latitude

CAM Photosynthesis:

Time & Place & How Accounts for Heat Dilemma

**Time separation** of processes

Adaption → **open** stomata at **times** they are **less likely** to **lose** water

\
^^Initial C fixation^^ → **mesophyll** (night) → open stomata & fix

^^Calvin cycle^^ → **mesophyll** (day) → close stomata & complete

CAM Photosynthesis:

Process

^^Night^^ → combine **CO2** w **PEP** (3C) → produce a **4C acid** → acids **stored** until daylight

^^Day^^ → **4C acids** broken into **CO2** & **pyruvate** (3C) → then enters **C3 pathway** (Calvin cycle)

How does CAM Photosynthesis Process Increase Water Efficiency?

Open stomata at night → **lower temps** & **higher humidity** → ^^reduce water loss during CO2 uptake^^

Label the Photosynthetic Process

A → **CAM**

B → **C4**

C → **C3**

Chemoautotrophs thrive on nutrients from --A-- & often live in regions where --B--

A → **Hydrothermal vent** (deep sea)

Bacteria can **oxidize** these nutrient compounds → combine w carbon & undergo **chemosynthesis**

B → the **light doesn’t reach**

What are hydrothermal vents?

What do they release?

**Fissures** in the **sea floor** (along oceanic rifts) → release **H2S** & **heat**

What are the primary producers in chemosynthetic environments?

Often **chemoautotrophic bacteria** act as primary producers support rich life

Chemo**litho**autotroph vs Chemo**organo**autotroph

^^Chemo**litho**autotroph^^ → derives E from **oxidizing** compounds of **inorganic** origin (eg. H2S, Fe2+, NH3, NH4+)

^^Chemo**organo**autotroph^^ → derives E from **oxidizing** compounds of **organic** origin (eg. CH4, etc.)

What is the chemosynthesis reaction?

**2 H2S + O2 → 2 S0 + 2 H2O + Energy**

H2S → from vents → bonds rich in E

S0 → elemental sulfur

Energy → used to synthesize organic molecules using CO2 as C source