Plant physiology, Plant physiology, growth and roots growth and roots

Effects of the environment

This means that all other organisms rely on plants.

Later experiments showed that plants

actually make their own food!

This was proved to be untrue by measuring the mass of the soil in a plant pot before and after growth. The soil did not decrease in mass, even though plant mass increased.

Do plants eat soil?Do plants eat soil?It used to be thought that plants got their food from the soil.

What is the name of the process by which plants make food?

Plants are the only living organisms that can do this.

PhotosynthesisPhotosynthesis

Plants make their own food by photosynthesis.

PhotosynthesisPhotosynthesis

light energy

This process is a chemical reaction that uses light energy.

light energy

chlorophyll

carbon dioxide + water oxygen+glucose

PhotosynthesisPhotosynthesis

Take a look inside a leafTake a look inside a leaf

How do gases enter and leave How do gases enter and leave plants? plants?

On the underside of leaves are small holes, or pores, called stomata. A single hole is called a stoma. Each stoma is surrounded by two guard cells.

When guard cells gain water, they curve outwards. This opens the stoma, allowing gases in and out.

Losing water causes the guard cells to come closer together, closing the stoma. This stops the movement of gases, but also prevents water loss.

Opening and closing of Opening and closing of stomastoma

RespirationRespiration

carbondioxideglucose oxygen water energy

GLUCOSE reacts with OXYGEN to produce CARBON DIOXIDE and WATER and stored chemical ENERGY is released.

A chemical reaction that takes place in all living cells.

Why do trees need energy?Why do trees need energy?

• Metabolism• Growth

– cell division and expansion• Reproduction• Chemical processes• Mineral uptake• Active transport• Defence

How do tall trees get enough How do tall trees get enough water?water?

How does a plant this size get water from its roots to the branches at the top?

The tallest redwood ever measured was 120 metres tall. That is six times the height of the Angel of the North!

TranspiratioTranspirationn

What is transpiration?What is transpiration?

Although it may seem bad for plants, transpiration actually moves water from the roots to the top of the plant, without using energy. How does this work?

Water always moves from an area of high concentration to an area of low concentration. This movement of water is a type of diffusion called osmosis.

Transpiration is the loss of water by evaporation from plants.

Plants lose water when they open the stomata in the leaves to let in carbon dioxide.

Air around the plant usually contains less water than the cells of the plant, so water evaporates into the air.

TranspirationTranspiration

RootsRoots

Root hairs

Mycorrhizae

Water uptakeWater uptake

Changing concentrationsChanging concentrations

The rate of diffusion depends on several factors, such as the distance the particles have to travel and the difference in concentration.

Molecules diffuse until they are evenly spaced apart and equilibrium is reached.

During diffusion molecules move from an area of high concentration to an area of low concentration. They are said to move down a concentration gradient.

Diffusion is a passive process which means that no energy is needed.

highconcentration

lowconcentration

What is osmosis?What is osmosis?

water

glucose

semi-permeablemembrane

Osmosis is the diffusion of water molecules from a low concentration solution to high concentration solution, across a semi-permeable membrane.

A semi-permeable membrane has holes in it that permit water molecules through but are too small to allow larger molecules through.

Dilute vs. concentratedDilute vs. concentrated

Concentrated solutions have a low concentration of water molecules.

Dilute solutions have a high concentration of water molecules.

During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions.

pure water dilute solutionconcentrated

solution

Predicting osmosisPredicting osmosis

Osmosis in actionOsmosis in action

What environmental factors will affect the rate of transpiration?

humidity (amount of moisture in the air)

light intensity

temperature

air movement (wind).

How do minerals enter How do minerals enter plants? plants?

Like water, minerals enter plants through the roots. However, they do this by different methods.

Water passively diffuses with a concentration gradient from the soil into the roots and up the stem.

Diffusion cannot take place against a concentration gradient.

Minerals are usually found in the soil in lower concentrations than they occur in the plant. Why can they not be transported by diffusion?

Instead, minerals enter the roots by active transport.

Active transport in plantsActive transport in plantsPlants need to absorb mineral elements such as nitrogen, phosphorus and potassium from the soil for healthy growth.

When the concentration of minerals in soil is lower than inside the plant, active transport is used to absorb the minerals against the concentration gradient.

What would happen if the plant relied on diffusion to absorb minerals?

The cells would become drained of minerals because they would travel down the concentration gradient.

minerals

What is active transport?What is active transport?

Which cells transport Which cells transport nutrients?nutrients?

Plants contain two types of cell adapted for transportation.

Phloem cells (sieve tubes) transport sugars produced in the leaves up and down the stem to growing and storage tissues.

Xylem vessels (tracheids in conifers) transport water and minerals up the stem from the roots to the shoots and leaves. This transport occurs in one direction only.

Both phloem and xylem form continuous systems connecting roots, stems and leaves.

How is xylem adapted for How is xylem adapted for transportation?transportation?

Xylem vessels have thick cellulose cell walls, strengthened by lignin. The inside of the cell is hollow. Xylem vessels are dead cells.

The thick walls of xylem cells also help support plants.

Xylem vessels transport water and minerals from the roots to the shoot and leaves. This transport only occurs in one direction.

TranslocationTranslocation• Sucrose is pumped in

to sieve tube elements by companion cells.

• Sucrose loading requires energy.

• High sugar concentration in sieve elements (phloem), causes water to flow in.

• Pressure builds and sap is forced downwards.

• Sugar unloading in roots also uses energy.

• Water flows out due to osmosis.

Phloem sieve tubesPhloem sieve tubes

• Living cells

StorageStorage

• Glucose is converted to starch only in living cells.

• Starch is insoluble and stored as grains within paranchyma cells (axial and radial) of sapwood and roots.

ReproductionReproduction

Sexual ReproductionSexual Reproduction

Reproduction in conifers

Asexual reproductionAsexual reproduction

• Layering• Cuttings• Suckering

GerminationGermination

Requirements for Requirements for germinationgermination

• Water • Oxygen • Temperature• Light or darkness• Period of dormancy

DormancyDormancy

Mechanical• Hard seed coats

– soaking in a solution of sulfuric acid

– soaking in hot water or immersing the seed for a short period in boiling water

– mechanical scarification

Embryonic– Requires a trigger

(usually cold moisture) in order to make it respond.

– Cold stratification subject seeds to cold storage in a moist environment

GrowthGrowth

Cell divisionCell division

Cambium cell division

Environmental factors affecting Environmental factors affecting growthgrowth

• Sunlight

• Temperature

• Water availability

• Carbon dioxide

• Oxygen

• Pollution

SunlightSunlight

• Increased light increased growth

• Plant hormones (auxins) collect on the dark side, so the plant turns to the light

Hormones and Hormones and phototropismphototropism

Hormones and geotropismHormones and geotropism

RootsRoots

RootsRoots

Root hairs

Mycorrhizae

Roots always grow towards water, which is a positive tropism.

Roots will grow sideways, or even upwards, towards water.Roots always have a stronger response to water than gravity to ensure that a plant gets the water it needs.

How do roots respond to How do roots respond to water?water?