Botany Exam 2

tap root system

dicots

fibrous root system

monocots

pneumatophores

specialized roots used for breathing (mangroves)

shoot region order + vascular tissues

root cap → cell division → elongation → maturation

(outtermost → innermost): ground meristem → endodermis → phloem → xylem

Epidermis function

outermost layer for absorption.
Produces root hairs to increase surface area

Cortex function

storage tissue

Endodermis function

The barrier for water and minerals
before entering vascular tissue

Pericycle function

Lateral roots emerge from this layer

Vascular bundle function

Transport of water and food

root tissue order (outer to inner)

epidermis → cortex → endodermis → pericycle → vascular bundle

Casparian strip

stops the non-selective absorption
of materials into a root from soil

lateral meristems

Dicot plants develop lateral meristems to increase girth (width)
by secondary growth

Lateral meristems are secondary meristems.
Secondary meristems and secondary growth are not seen in monocots

What is wood?

The secondary xylem is responsible for the “wood” in stems and roots of woody dicot plants

bark and wood diagram

lead anatomy diagram

alternate leaf arrangement

opposite leaf arrangement

whorled leave arrangement

dicot leaves

Reticulate venation
Petioles
Kidney-shaped stomata

monocot leaves

Parallel venation
Sheath-like leaf base
Dumbbell-shaped stomata

venation

an arrangement or system of veins

upper epidermis of leaf

- usually coated with a waxy cuticle
- contains few stomata

mesophyll cells of leaf

- The main photosynthetic tissue
- arranged as palisade and spongy in dicots

- undifferentiated in monocots

lower epidermis of leaf

-thinner cuticle
- contains many more stomata

the mid-rib of a leaf contains the

vascular bundle

palisade parenchyma

converts the light energy to the chemical potential energy of carbohydrates.

spongy parenchyma

allow for the interchange of gases (CO ₂) that are needed for photosynthesis, photosynthesis

typically the stomata on a leaf are located in the

lower leaf epidermis

stomata purpose

gas exchange, transpiration occurs through these

stomata’s guard cells use

turgor pressure to open and close, turgid → open flaccid → closed

subsidiary cells surround the

stomatal guard cells

Guard cells and subsidiary cells work together to

regulate the K+ ion concentration

Xerophytes

(arid climate plants) Shiny surface
Thick waxy cuticle
Trichomes (hairs)
Sunken stomata (stomatal crypts)
Multi-layer epidermis
Sunscreen chemicals in the epidermis
There are no stomata in the upper
epidermis

Hydrophytes

ex. water lilies

Many air spaces stomata only in the upper epidermis
Very little xylem tissue
Water-repellant coating on the epidermis

Bulliform cells

specialized for grass blades, closes the leaves when flaccid, opens them when turgid

Bracts

“false flowers” brightly colored leaves to attract pollinators ex. poinsettia

Bulbs

The bulb is a short underground stem with fleshy leaf bases
surrounding it, used for food storage ex. onions

Spines

modified leaves to conserve water and used for defense ex. cacti spines

spines are, thorns are, prickles are

modified leaves, modified branches, modified epidermis (extended)

root system + shoot system relationship

roots absorb water and minerals, but need sugars for cellular respiration. shoots produce sugars via photosynthesis, but need water and minerals for photosynthesis and metabolic activities

vascular tissue is responsible for

long-distance transport of • Water
• Minerals
• Sugars
• Primary organic metabolites
• Hormones
• Secondary metabolites

The two conductive tissues of the vascular bundle are:

the phloem and xylem

xylem tissue function

transport water and minerals up the root and stem, into all aerial organs

the xylem tissue consists of:

Xylem vessels
Tracheids
Xylem fibers
Xylem parenchyma (only cells alive at maturity, does not have signified cell walls)

Xylem vessels and tracheids are for

water transport and strength (both contain lignified cell walls)

Xylem vessels

Wide, short barrels arranged in tandem with perforated end walls.
Pits on side walls to pass water laterally

Tracheids

Long, narrower cells with tapered ends that overlap.
Many pits on walls to pass water from cell to cell

lignin

a phenolic compound adds waterproof properties to cell walls
indigestible by humans/animals only certain bacteria and wood-rotting fungi have enzymes to digest lignin

Transpirational pull:

(evaporation of water from leaves pulls water up the stem during daytime) Used by all plants

Root pressure:

pushes water up the stem at night.
Used by shorter plants

Transpirational pull is possible due to two properties of water:

Water is cohesive
• Water is adhesive
Water molecules attract to each other by hydrogen bonds
Water molecules adhere to hydrophilic surfaces like cell walls

Transpirational pull is explained by

Cohesion – tension theory

Cohesion-tension theory

In the presence of a tension of a pull due to transpiration, the cohesion of water molecules allows them to form a continuous column

guttation

result of root pressure, accumulation of minerals and water on the tip of leaves

Hydathodes

push a droplet of water out due to positive pressure

Both transpirational pull and root pressure are essential
for plants to;

1. Get a supply of water for turgor, photosynthesis, and hydration of tissues in general
2. Get a supply of minerals necessary to maintain
cellular functions (i.e. enzyme activities, structure)

Macronutrients in plants

N, P, K, S, Ca, Mg (C,H, and O are also considered extremely important but not macro or micronutrients)

Micronutrients in plants

Fe, Mn, B, Cl, Zn, Co, Mo

Nitrogen deficiency

Older leaves become yellow, by mobilizing N to young leaves during deficiency

Iron deficiency

Young leaves become yellow because iron is not moved from older leaves during deficiency

Phloem tissue in the vascular bundles is responsible
for

transport of food and other organic compounds

Phloem tissue contains;

Sieve tube elements
Companion cells
Parenchyma cells
Phloem sclerenchyma fibers – dead at maturity

Sieve tube elements

live cells with “no nucleus” Nucleus of the companion cell regulates sieve tube functions

Formation of sieve tube elements and companion cells

Formed by asymmetrical division
Sieve tube elements lose most of the cytoplasmic structures and the nucleus, leaving more room for bulk transport

Transport of sugars and organics happens by

“mass-flow”
(bulk-flow) through sieve tubes from source to sink

Phloem loading

Sugars loaded to sieve tubes in leaves by companion cells
- Osmosis brings water from nearby xylem tissue
- Pressure builds up in the sieve tube
- Sap is pushed down to the next sieve tube element

Phloem unloading

- When sugars reach roots they are unloaded from sieve tubes
- Water moves back to the xylem by osmosis

Photosynthesis:

Happens in the chloroplasts of all green tissues.
The ultimate source of food for both plants (directly) and animals (indirectly)
Generates oxygen for aerobic cellular respiration

Photorespiration:

This happens in the chloroplasts of many plants as a wasteful process
Reduces the efficiency of photosynthesis
Some species have evolved counter mechanisms to minimize the harmful effects of photorespiration

General reaction of photosynthesis

made up of light dependent and light independent reactions

Light dependent reactions –

Pigments capture light energy and use it to make chemical bonds
Water breaks down and provides electrons

Light independent reactions –

(Calvin Cycle) Use the products of light reactions to fix CO2 into
sugars

Chlorophyll a

reflects green light

Chlorophyll b

reflects some green and yellow

carotenoids:

carotene and xanthopylls

carotene

reflects orange and yellow

xanthophylls

generally reflects a bit less of the same colors as carotenes

thykaloids

carry photosystem II and photosystem I, perform light reactions

a stack of thylakoids is called a grana (inside the chloroplasts)

stroma

liquid inside chloroplasts, contains enzymes to carry out the Calvin cycle to fix CO2

Photosystem II and PS I

produces NADPH+, ATP, and 2 electrons to be used for the Calvin cycle via the electron transport chain, antenna pigments bounce electrons along to do so

PSII and PSI require

H2O to breakdown, producing 2 electrons to continue along the electron transport chain, this breakdown also produces oxygen

the electron transport chain occurs inside the

thykaloid

Summary of light reactions:

Use: light energy, H2O
Produce: ATP and NADPH
Release: O2

ATP and NADPH are needed for

for the Calvin cycle.

Rubisco enzyme

catalyzes CO2 fixation in Calvin cycle

The first organic compound produced from CO2 is the

3 carbon Phosphoglyceric acid (PGA)

C3 photosynthesis is called so due to

the production of PGA, a three carbon compound produced at the beginning of the Calvin cycle

C3 photosynthesis is inefficient due to

occurrence of photorespiration in C3 plants

C3 plants:

All seedless plants
All Gymnosperms
95% of dicots
60% of monocots

Photorespiration occurs because

O2 rich atmosphere, O2 binds to rubisco, inhibiting Calvin cycle (occurs at higher rates in hot, dry climates), decreases the output of carbon

C4 pathway:

Separates O2 releasing PSII from Calvin cycle
CO2 is concentrated in cells that perform the Calvin cycle, About 5% of dicots and 40% of monocots have evolved C4 photosynthesis

C4 mostly occurs in

hot, dry climates that promote photorespiration

C4 utilize:

specialized “kranz” anatomy

C4 mechanism:

Mesophyll cells fix CO2 into 4-carbon oxaloacetate and then into malate

Malate travels to bundle sheath cells, allowing Rubisco and the Calvin cycle to carry out, malate breaks down, releasing CO2 required for Calvin cycle

C4 reduces photorespiration via

carrying out PSII and PSI, but no calvin cycle in the mesophyll cells → producing malate → and the bundle sheath cells carrying out only PSI and Calvin cycle (isolates the Calvin cycle and rubisco from O2, increasing efficiency)

Examples for C4 plants:

sugarcane,
corn
sorghum

CAM pathway

CAM pathway conserves water by opening stomata at night , Crassulacean Acid Metabolism

CAM pathway mechanism:

stomata close during day (less water loss), plants perform Calvin cycle and light dependent reactions, malate breaks down for CO2 → stomata open at night, plants take in CO2 fix into oxaloacetate then breaks down to malate, malate is then stored in the vacuole.

CAM pathway acidity

plant will become more acidic at night and more neutral during the day

C4 pathway plants vs. CAM pathways

Physically separated
Happens in different cells

vs.

Temporally separated
Happens in the same cell