plant form & function

autotrophs

ultimate source of all biological energy

three main groups of plants

nonvascular plants, seedless vascular plants, seed plants

plants left the water because there was more … on land

more light (more photosynthesis potential) and more CO2 (easier CO2 uptake for photosynthesis)

challenges in plant transition from water to land

• 1. Protection from UV radiation

• 2. Staying upright

• 3. Retaining moisture (avoiding

• desiccation)

• 4. Transporting water and

• nutrients

• 5. Reproduction without water

to avoid UV damage

plants accumulated flavonoids that protect plant tissue from constant UV exposure

to stay upright

plants evolved rhizoids (underground stems), roots, lignin/cellulose (compounds that harden cell walls),

tap-root system

root system good for a deep water table, infrequent/low amounts of precipitation, extended periods of drought

fibrous root system

root system that is shallow and fast absorbing

xylem

vascular tissue that conducts water and dissolved nutrients upwards from roots via capillary action

phloem

vascular tissue that primarily conducts sugar downwards from leaves

to prevent water loss from tissues

waxy cuticle layer formed & stomata

waxy cuticle layer

Watertight sealant that covers the aboveground parts of the plant to protect from desiccation the extreme drying out of an organism or tissue due to loss of water)

stomata/stoma

used for gas exchange; the stomatal opening (pore) opens and closes as guard cells change shape to control gas flow

stomata are found on

the bottom surface of leaves (to reduce H2O loss from evaporation, while still allowing gas exchange)

trade-off between gas exchange in stomata

Plants need to balance CO2 uptake with H2O loss

conditions for when stomata opens

stomatal density

 # stomata per unit area on a leaf 

Stomata in a high CO2 environment:

less stomata, CO2 is easier to get, avoid unneeded water loss

stoma in low CO2 environment

 more stomata, co2 is harder to get & plants need to maximize intake

for plant reproduction on land

spores, protective tissues, seeds, flowers

spores

resist drying because they are encased in a tough coat (sporopollenin)

Protective tissues:

nourish embryos

seeds

Fertilized ovules that contain an embryonic plant, stored nutrition for the embryo, and protective coatings 

seeds can facilitate dispersal and allow for dormancy (gene flow)

Can increase fitness by preventing germination until conditions are favorable

two main groups of seed plants

Gymnosperms & Angiosperms 

gymnosperms

do not produce flowers or fruit, found in drier environments, narrower tracheids (xylem tubes) (ex: confers, produce cones rather than fruits, have modified, drought-resistant leaves)

narrower tracheids (xylem tubes)

less efficient at transport, BUT are resistant to freezing & drought 

fruit

• structure that houses the seed during development

• develops from ovary or surrounding tissue

• Provides protection and aids dispersal

angiosperm structure

angiosperms

flowering plants, seeds enclosed in an ovary/fruit, categorized based on morphological structure

types of angiosperms

monocots, dicots

monocots

• Primarily tropical distribution, but also found in coastal marine environments, deserts, streams & ponds, and the arctic tundra 

• Most large floating & submerged aquatic plants

• includes epiphytes (plants that grow on other plants (usually on branches or trunks) without harming them.)

dicots

• All of the non-conifer woody plants are dicots

• Widely distributed across habitats 

• not a monophyletic group!

structural differences of monocots and dicots

major innovations in plants

1. Chloroplasts containing chlorophyll

2. Multicellularity

3. Embryo protection

4. Cuticle (stomata, vascular tissue, roots)

5. Seeds 

6. Flowers

root and shoot systems

acquire resources for photosynthesis

shoot systems

• Harvest light and CO2 from the atmosphere for sugar production

• Vascular tissue provides the connection for the transport

root systems

• Anchors the individual in palace 

• Uptake water and nutrients

limiting resources for photosynthesis

• Water (deserts)

• CO2 (when stomata is closed)

• Light (shady forests/cloudy/alpine areas)

environmental factors that affect photosynthesis

• Temperature 

• Nutrient availability

• Water availability/humidity 

• Wind/gas exchange

• Soil conditions 

plant adaptations to deal with diff environments

• Dry Environments 

  • Close stomata more, thick cuticle, CAM

• Low light environments 

  • Larger, thinner leaves 

  • More chlorophyll

• Cold environments 

  • Slower metabolism

  • Short growing seasons

  • Specialized enzymes

photosynthesis

process that is used to store light energy in C-C bonds as carbohydrates (sugars)

• Multistep process to gather CO2 and water & use particular wavelengths of light to create sugar and O2

• Performed by autotrophs

3 Main Photosynthetic Strategies

C3, C4, CAM

C3

• all purpose photosynthesis 

  • Not good in hot & dry conditions (too much water loss)

C4

•  takes more energy, but more efficient than C3 photosynthesis 

  • Works well in hot & dry climates

  • CO2 is fixed by PEP carboxylase (instead of rubisco)

CAM

• similar to C4 photosynthesis but saves even more water

  • Found in desert plants with extremely limited water

  • opens stomata at night

  • time restriction reduced total primary productivity

photosynthesis occurs in leaf tissue

mesophyll

mesophyll

• internal tissue between the two epidermal cell layers of the leaf 

light-dependent reactions

harvest solar energy & create ATP and reduced electron carriers (occurs in thylakoid)

calvin cycle

use stored chemical energy (ATP) to generate G3P (occurs in stroma)

two stages of photosynthesis

photosynthesis is most efficient in these wavelengths

• ✅ Blue light  (~400–500 nm)

• ✅ Red light (~650–700 nm)

• ❌ Green light (~500–600 nm): mostly reflected → why plants look green

in hot temperatures Rubisco can react with

O2 instead of CO2 leading to photorespiration

key differences in C3, C4, CAM

visual comparison of C3, C4, CAM

photosynthetic light response curve

photosynthetic temperature response curve

effect of CO2 photosynthesis