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9.1 Specialized and Organized
In single-celled organisms, one cell must be able to perform all the _functions_____ of life, whereas many cells work
together to meet the needs of a _multicellular____ organism.
Cell Specialization in Leaves
Define photosynthesis- Chloroplasts inside leaf cells contain chlorophyll which traps light energy. This energy is used to
drive chemical reactions that produce glucose and oxygen.
Define glucose- Glucose is a carbohydrate that both plant and cells and animal cells use as a source of energy. Plants can
synthesize through photosynthesis while animals must ingest it in food.
Sketch and label chloroplast and describe how photosynthesis occurs. (Figure 9.2)
YOU DO NOT NEED TO MEMORIZE ALL OF
THIS DIAGRAM!! Here’s what’s important:
chloroplasts are the site of photosynthesis. There
are 2 parts of photosynthesis (I and II). In
photosynthesis I, light and water are consumed and
oxygen is produced; in photosynthesis II, carbon
Photosynthesis I
Photosynthesis II
dioxide is consumed and glucose (sugar) is
produced. It is also important to know that
photosynthesis occurs in the leaves of the plant.
Define chlorophyll- Chlorophyll is a pigment found in chloroplasts which traps light energy for photosynthesis.
Draw and label a cross section through a leaf. (Page 321)
Upper
Lower
Epidermis
Stomata
Cell, Tissue, Organ, System
List three advantages multicellular organisms have over single-celled organisms.
1. larger size
2. variety of specialized cells
3. thrive in a broader range of environments
There are multiple levels of organization in organisms; from most basic to most complex, they are: ___cells________,
____tissues________, _______organs___ and ____systems_______.
Give an example of a plant tissue: epidermal tissue, vascular tissue, ground tissue (I don’t think your textbook mentions
ground tissue)
Give an example of a plant organ: roots, stems, leaves
Give an example of a plant system: vascular systems for water and sugar transport
9.1 Cell Specialization in Leaves
cuticle
Upper
epidermis
What to Do
Label the specialized leaf cells in the diagram below.
Then write a brief description of the function of each
leaf cell.
Palisade layer
xylem
phloem
Lower epidermis
stomata
Guard cells
Spongy mesophyll
A. Upper epidermis – layer that protects and covers the upper and lower surface of the leaf
B. Palisade layer – long, narrow cells that are packed with chloroplasts; site of most of photosynthesis in the leaf
C. spongy mesophyll – below palisade layer; round shape, which helps them exchange gases and water with the
environment; site of some photosynthesis
D. stomata – small openings that allow gases in and out of the leaf
E. xylem – vascular tissue that carries water and dissolved minerals from roots to the rest of the plant
F. phloem – vascular tissue that carries sugar from the leaves to the rest of the plant
G. guard cells – cells that flank stomata; size changes to open or close stomata
H. cuticle – waxy substance that coats cells to prevent evaporation of water from the leaf
9.2 Gas Exchange in Plants
Diagram and explain how plants exchange gases with their environment.
Gases diffuse through the cell membrane of the spongy
mesophyll layer. Oxygen diffuses out of the spongy mesophyll
cells and is released from the leaf through the stomata. Carbon
dioxide enters the leaf through the stomata and diffuses into the
spongy tissue. Water, which enters the leaf through xylem, exits
through the stomata as vapor.
Something in the Air
What do plants consume and produce during cellular respiration?
Consume: some oxygen and glucose
Produce: some carbon dioxide and water vapor
What do plants consume and produce during photosynthesis?
Consume: carbon dioxide and water
Produce: oxygen and glucose
Leaves and Lenticels
How does carbon dioxide enter the leaf for photosynthesis to occur?
Carbon dioxide enters the leaf through the stomata and moves by diffusion into the spongy mesophyll
tissue and palisade tissue where it is used for photosynthesis.
Define lenticels:
In woody plants, layers of dead cork cells and waxy substances prevent direct gas exchange. Lenticels
are lens-shaped openings that perforate bark, allowing air to diffuse into the roots and stems.
Gas Exchange is tied to Water Loss
Plants lose __water________ during gas exchange.
Define transpiration:
The evaporation of water from the leaves.
Evaporative cooling, through transpiration, can prevent heat _damage____ to plants. If plants lose so much
water through transpiration, what keeps these plants from exhausting their water reserves?
Guard cells close stomata so less water is lost.
Define turgor pressure:
Turgor pressure is water pressure that pushes the elastic cell membrane against the rigid cell wall.
Enough pressure causes guard cells to change shape, allowing stomata to open.
Give one reason why crop yields are lower during droughts:
During droughts, stomata are closed to conserve water (reduces transpiration). However, the closed
stomata also prevent carbon dioxide from diffusing into the leaf, which prevents the production of
sugar from photosynthesis, which reduces the growth of the plant (crop, in this case).
Why do houseplants go limp if they are not watered often enough?
Reduced watering reduces turgor pressure which is what keeps non-woody plants firm and rigid
9.3 Water Transport in Plants
Within individual cells, water is transported mainly by _osmosis_______
Xylem Vessels and Phloem Vessels
What are the two types of specialized tissues that make up a plant’s vascular system? Xylem and phloem
The xylem tissue transports ____water____ and dissolved _______minerals_____ from the soil to the
____leaves______.
Define xylem vessels:
Xylem vessels are linked tubes of hollow, dead cells that consist mainly of the cell walls. They are the tubes
through which water and minerals flow
The phloem tissue transports _sugars_____ produced during _photosynthesis___ throughout the plant.
Define phloem vessels:
Phloem vessels are tubes formed by cylindrical cells joined end to end; the cell walls of these cells are porous to
allow exchange with the environment
Unlike xylem, phloem cells are _living_.
Maple syrup is made from a sugary sap that is tapped from maple trees. Where is the sap produced in the tree? What part
of the tree is tapped for the sap?
The sap is produced during photosynthesis (sugar production) which happens in the leaves. The sap is then
transported by phloem; you would tap a phloem vein in the stem/trunk of the tree to collect it.
Define tracheids (a.k.a. vessel elements):
Tracheids are long, hollow cells within the xylem vessels. They begin as living cells but die after maturation,
leaving only cell walls.
Define sieve tubes & companion cells:
Sieve tubes and companion cells are terms used to identify components of phloem tissue; they are connected in long
tubes to make phloem vessels.
Water Uptake in Roots
__Epidermal_ tissue covers the root and the epidermal cells are _permeable_ to water.
How does water enter the cells of the root epidermis? __Through root hairs__
Define root hairs:
Root hairs are tiny, thin projections of roots that increase the surface area of the root so that water and mineral
absorption is maximized.
Why are root hairs important?
Root hairs are important to maximize the amount of water and minerals that can be absorbed into the plant.
How do minerals enter root cells? (Discuss two methods depending on concentration gradients)
If the minerals are moving into the plant along (down) their concentration gradients, then they are moving by
facilitated diffusion. If they are moving against (up) their concentration gradients, then active transport is required.
Define xylem sap:
Xylem sap is the solution of water and minerals that accumulates in the root xylem.
What direction does the xylem sap flow? __Up – from the roots to the stems and leaves
Properties of Water
Compare and contrast cohesion and adhesion.
Cohesion is the tendency for water to stick to other water molecules
Adhesion is the tendency for water molecules to stick to other substances; allows water to move upwards through the
plant against gravity.
Root Pressure Pushes
Define root pressure:
Root pressure is the force that pushes fluids upward from the roots towards the leaves against gravity.
What increases the tendency for water to diffuse into root xylem and how does this influx of water contribute to root
pressure?
As mineral concentration increases in the root xylem, water flows in by osmosis (trying to achieve equilibrium). Water
flowing into the root xylem increases root pressure thereby forcing fluids upwards from the roots.
Transpiration Pulls
If root pressure can only move water upward a few meters, how does water get to the tops of tall trees and plants?
Water is pulled up by the transpiration (evaporation) of water from leaves; a tension is created that pulls the water
column in xylem from the roots. The water column is held together by cohesion; adhesion keeps the water column in
place.
Sugar Transport in Phloem
The sugars produced by the _palisade__ tissue cells and the __spongy_ tissue cells provide energy for the whole plant.
In what direction does the phloem sap flow? _downwards (from leaves to roots)_
Sugar, minerals and other nutrients are pumped into the leaf phloem by _active_ transport.
Define phloem sap:
Sugar, nutrient, and water mixture. Some water is transported into the phloem by osmosis.
Check Your Understanding
1. Will a daisy plant transpire more in a humid environment or in a dry environment? Explain your reasoning.
When the air that surrounds a plant is dry, the water osmosing out of a leaf will occur more rapidly (transpiration will
occur more rapidly than in a humid environment)
2. Explain why root pressure alone cannot transport water from the roots to the leaves of most stems.
Root pressure, above a few meters, is not strong enough to keep pushing water up against the force of gravity.
3. If the stem of a plant is bent or snapped, the part of the plant above the bend will usually die, even if it is propped
up with a support. Explain why.
If the stem is bent or snapped then vascular tissue is damaged. Even if it is propped up, the damaged cells can no longer
provide enough support for the flow of water, sugar, and minerals; the adhesive force has been compromised.
DATE:
NAME:
CLASS:
BLM 9-3
REINFORCEMENT
Gas and Water Movement in Leaves
Goal  Review the movement of gases and water in leaves.
What to Do
Answer each question in the space provided.
1. On the diagram below, label the movement of oxygen, water, carbon dioxide, sugar, and minerals.
Water & minerals
sugar
CO2
O2
2. Briefly describe the movement of water, gases, and minerals through a plant leaf.
Water and minerals enter the leaf through the root xylem. Sugar exits through the phloem. Carbon dioxide
enters the leaf through the stomata; water and oxygen exit the leaf through the stomata.
3. Explain the role of the cuticle and stomata in movement of water in a leaf.
The size of the stomata affects the amounts of gases that are exchanged. The cuticle protects the leaf and helps to
prevent the evaporation of water from the leaf.