Biodiversity in the Sonoran Desert

Unit 3, (10/01)

Where is the Sonoran Desert located?

Southwestern US and Northwestern Mexico

Describe the growing season in the desert? When is the best growing season?

• summer is too hot (95 F) for plants to grow well (also not wet enough)

• spring is too dry

• winter is the ONLY good growing season for many plants, especially annuals

What are annuals?

• plants that germinate, grow, set seed, and die in a single growing season

Describe the climate change in the Sonoran Desert

• temperature is going up

• rainfall is going down 

Describe the relationship between climate change and precipitation 

• distribution of precipitation changes spatially and temporally

• more episodic (less frequent and more intense)

• more floods and droughts (storms)

How much of the Earth’s biomass do plants make up?

80%

What molecule (not atom) makes up most of a plant’s biomass (besides water)?

cellulose

Where does the carbon in cellulose in a plant come from, the air or the soil?

the air

What was the purpose of Von Helmont’s experiment in the 1600s? 

He was trying to figure out where the carbon in his willow trees was coming from 

What plant organ obtains water?

roots

what plant organ creates sugar used for growth?

the leaves

What plant organ collects light?

the leaves

if you want to be able to grow fast (cellulose), where should you allocate resources? 

the leaves

if it’s dry, where do you want to allocate resources?

root system

if there are a lot of plants growing around you and you are in danger of being light limited, where do you want to allocate resources?

the stem

What is the basic (unbalanced) reaction for photosynthesis? 

CO2 + water + sunlight → glucose + O2

Besides photosynthesis, why is water important for plants?

• structure

• tugor pressure and osmosis (how water makes a plant stand up)

What is Tugor Pressure?

• how water makes a plant stand up

• created when the valcoule, full of water, exerts outward pressure on the cell wall

What does turgid mean? What does flaccid mean? 

• turgid = rigid plant

• flaccid = wilted plant 

What does the Physics of Equilibrium state?

• things move from HIGH to LOW: concentration, pressure, temperature (cold → hot bc cold gases are more dense), and charge (highly charged to no charge)

Describe Passive Transport

• none of these require ATP

• potential energy → kinetic energy

• Examples: osmosis, simple diffusion, and facilitated diffusion

Define Diffusion 

• movement of molecules from HIGH to LOW concentration 

• ex. of passive transport 

Define Osmosis

• movement of solvent (water) across a semipermeable membrane from HIGH to LOW solvent concentration

• ONLY solvent (water molecules) moves

True or false: water concentration and solute concentration are opposites?

• True

• dilute = high H2O, low solute

• concentrated = low H2O, high solute

In diffusion, we are usually focused on the movement of _____ molecules 

solute

In osmosis, we are focused on the movement of _____ molecules, water specifically

solvent

What makes osmosis different from regular diffusion?

the presence of a semi-permeable membrane that allows water through

Describe turgid cells

• water enters by osmosis, vacuole swells and pushes against cell wall

Describe flaccid cells 

• water lost from cell, vacuole shrinks, cell loses shape

What is intercellular space?

the space between cells

Where does water enter and exit a plant?

• water enters through the roots and exits through the leaves (stomata)

What is the transport system in plants made up of?

• vascular tissue: xylem and phloem

Describe the phloem?

carries dissolved nutrients, hormones, sugars, etc. around a plant in any direction using osmosis

Describe the xylem?

• carries water through hollow, “dead” cells from roots to leaves ONLY; “one-directional “straws”

Xylem tissues transport water passively using?

• cohesion - water sticks to other water molecules (H bond)

• adhesion - water sticks to other molecules 

Why do plants need water in their leaves?

• that’s where photosynthesis happens!

• xylem extends into the leaves where water becomes water vapor in the space btwn cells

• water vapor exits through the stomata

Describe the stomata

*gaps in the leaf that open and close using guard cells

What does it mean when the stomata is open?

water escapes

What does it mean when the stomata is closed? 

water stays in leaves 

As water escapes out the stomata, what is created?

• a tiny vacuum is created (negative pressure)

What direction does pressure move in?

pressure moves from high to low

True or false: high pressure H2O in xylem is drawn to the low pressure in leaves

true

True or false: negative pressure is responsible for water being drawn up to the leaves? 

• true; pulling up creates negative pressure, forcing the liquid to move up into the syringe where there is low pressure

• pushing down creates positive pressure by increasing the pressure in the syringe, forcing liquid out 

Water moves in plants for a variety of reasons, such as?

• phloem (osmosis)

• xylem (negative pressure)