Science Focus 10 Unit 3
Cycling of Matter in Living Systems p.254-359
In this unit we will explore:
 microscope technology
 the cell theory
 cellular structures and function
 cellular transport
 The specialized cells of multicellular organisms
 plant cell mechanisms (gas exchange, water transport)
Chapter 7: The Basis of Life p.258
7.1 Life From Life
The development of the theories of the origin of living matter:
A.
Aristotle (384 BC – 322 BC) – a Greek philosopher whose theory of abiogenesis or spontaneous generation was accepted for over 2000 years.
Abiogenesis – living things could arise from non-living matter
Examples: a) eels came from the slime in river mud b) rats came from garbage or dirty laundry c) maggots came from rotting material d) mice came from a pile of wheat husks e) frogs came from mud

Aristotle created his theories on the origin of life based on his many observations, however, he did not conduct any scientific experiments to test his ideas.
Q: Choose one of the above examples and describe how to refute the idea using scientific experimentation.
B.
Francesco Redi (1626 – 1697) – Italian physician who used controlled scientific experiments to refute the theory of spontaneous generation
Redi’s experiment: see figure 7.2 p.259
Jar 1: meat, left uncovered -> maggots appeared
Jar 2: meat, covered in cloth -> no maggots appeared
Maggots appeared in Jar 1 because _____________
________________________.
NOTE: Within a few years, the discovery of microscopic single celled organisms, renewed the idea of abiogenesis. People believed a “vital force” or “active principle” in the air created these microorganisms.

C.
Louis Pasteur (1822 – 1895) – French scientist who finally settled the continued debate of the theory of abiogenesis.
Pasteur’s experiment:
< --------- airborne _________
settled here a) a swan-neck glass flask (figure 7.3) full of nutrientrich broth was boiled to force out air and kill any microbes b) flask was cooled and broth remained clear even after many days because any microbes entering, settled with gravity in the neck of the flask. c) When flask was tipped so broth reached neck, soon broth became cloudy. Explain: ________________
_______________________________________

As a result: The accepted theory became biogenesis
– living things could only arise from other living organisms (suggested by Vichow in 1858)
*WORD Biogenesis - Latin root “bio” = of living
CONNECT things and “genesis” = origin
Discovering Cells
Prior to seeing bacteria, the common assumption was that curses or supernatural spirits caused diseases!
The invention of the microscope allowed scientists to magnify objects and examine the microscopic world, and as a result, cells were discovered.
Cell – the smallest functional unit of life found in all living organisms
See cells Figure 7.4 p.261
TRIVIA
(p.265) * The largest cells are egg cells (largest: ostrich eggs which are 1.2 kg, 14 cm wide)
* The longest cells are nerve cells (longest is the sciatic nerve that runs down your leg)

Developing the Cell Theory
the cell theory explains and defines the boundary between the living and non-living and is integral to our understanding of life on Earth
The molecules that are food for a cell and the organic molecules that make up a cell are non-living, yet the cell is ALIVE!
A.
Robert Hooke (1635 – 1703) – looked at cork with a compound light microscope (30X magnification) and was the first to see and name “cells”.
B.
Antony van Leeuwenhoek (1632 – 1723) – Dutch linen merchant who first described single-celled microorganisms. He used a single lens microscope
(500X magnification) to study blood cells, pond water
& teeth scrapings
called his sightings “animalcules”
C.
Matthias Schleiden (1804 – 1881) and Theodor
Schwann (1810 – 1882) – German scientists who studied cells in hundreds of plants and whose research

contributed to the cell theory, stating that “all organisms are made of cells ”
(NOTE: they still believed that cells were created by spontaneous generation.)
D.
Rudolf Vichow – German physician who made microscopic observations of cells dividing and completed the cell theory still accepted today.
The Cell Theory
1.
All organisms are composed of one or more cells.
2.
The cell is the smallest functional unit of life.
3. All cells are produced from other cells.
Do Check Your Understanding p.265 #1, 2, 3, 6, 9
Do 7.1 Review Worksheet
7.1 Quiz on __________________

Science Focus 10 Unit 3 Chapter 7
7.2 Cells and Technology p. 266
A.
Light Microscopes – use to view objects illuminated by visible light
1.
Simple microscope – used only one lens (similar to a magnifying glass)
2.
Compound microscope – uses two or more lenses placed one on top of the other
first created on 1595 by Zacharias
Janssen, a Dutch maker of reading glasses
commonly has one lens in the eyepiece and one in each objective
can magnify as much as 2000 X
B.
Electron microscope – specimens are illuminated with a beam of electrons instead of a beam of light
magnifies up to 1.2 million times
electron micrograph – the photograph of the image produced by an electron microscope a) TEM – transmission electron microscope

built in 1931 in Germany
specimens are thinly sliced, then placed under a vacuum to remove moisture & particles.
Electrons are then transmitted through the specimen to view 2-
D internal structures & details. b) SEM – scanning electron microscope
designed in 1930’s in Germany
a beam of electrons sweeps over an object to create a 3-D image
(only the surface can be detected) c) CLSM – confocal laser scanning microscope
invented in the 1960’s
a laser beam directed at numerous planes creating a series of 2-D images or “optical slices”
computer software then “stitches” images together d) STM – scanning tunnelling microscope
invented in the mid-1900’s
enables scientists to obtain an image of atoms on an object’s surface (eg. DNA molecule)
a fine metal probe emits electrons towards specimen’s surface and information is interpreted by a computer producing a 3-D image
Do: Microscope Review Worksheet

Science Focus 10 p. 272 7.2 A Molecular World
Genes – sections of DNA that direct the activities of our cells
changes in the gene can cause improper cell function
eg. Sickle cell anemia
DNA – carries all genetic information of the organism, coiled to form chromosomes, found in the nucleus of every cell
constructed of 4 bases:
Adenine pairs with Thymine
Cytosine pairs with Guanine
the order of thousands of pairs of bases make up each organism’s unique genetic code
Q: Fill in the missing bases on this piece of DNA.
Gene sequencing – mapping the order of all of a gene’s bases
Human Genome Project (HGP) – an international project to sequence all 30,000 to 40,000 human genes
sequence information can be used to diagnose and treat genetic disorders

eg. gene therapy – human gene is “corrected” to help cure a disorder or cancer
Demo: Extract DNA from pea soup
Cancer - most cancers are caused by gene damage,
some of which create mutations
cancerous cells divide indefinitely and form
layers upon layers to form a tumor
Mutations – changes in the base sequence of a gene
- some mutations may cause a cancer where cells grow and divide uncontrollably forming a tumor
(SEE Fig. 7.15, p. 274)
Living or Not?
Virus – non-cellular structure made of a piece of genetic
material enclosed in a protein coat
in order to reproduce, a virus must infect a cell and use this host cell’s organelles (cell parts)
Prion – a protein that can convert into a harmful particle which can reproduce in living tissue
cause BSE (bovine spongiform encephalopathy) or “mad cow disease”
Culturing Cells

Cell culture – isolated cells are given nutrients and their
growth and division are studied
Cell lines – the generations of cells produced from a
culture; can be grown indefinitely in a lab
Eg. HeLa cells
Stem cells – “blank slate” cells that divide to produce all other types of specialized cells
found in: a) one week old embryos (aborted fetuses) b) adult bone marrow (these form different types of blood cells) c) unused embryos from in vitro fertilization treatments d) cord blood (from umbilical cord after birth) e) genetically engineered from human egg cells
mature into specialized cells which can only reproduce to form more of their own kind
(liver cells -> liver cells)
scientists hope to grow tissues and organs for transplants and to cure diseases using stem cells (eg.
Parkinson’s, Alzeimer’s, diabetes & spinal cord injuries)
Rudolf Virchow – the first scientist to link illnesses to malfunctioning cells

Science Focus 10 Unit 3 p.277 7.3
What’s in a Cell?
Cells – sustain life by performing the tasks essential for the cell to function: a) obtain food & energy b) convert energy (eg. photosynthesis) c) construct & maintain the molecules making up the cell structure d) carry out chemical reactions e) eliminate wastes f) reproducing
Organelles – internal cell parts that carry out specific functions
Prokaryotes – one-celled organisms lacking a membranebound nucleus & organelles (do contain ribosomes)
are the most abundant cells on Earth
eg. bacteria and algae
Eukaryotes – cells with a more complex internal structure including a membranebound nucleus & organelles
eg. most plant and animal cells
In Latin: “karyon” means nucleus
“pro” means before
“eu” means true therefore: prokaryote means before nucleus.
eukaryote means true nucleus.

Cell Organelles
1.
Cell membrane (plasma membrane)
a protective barrier for the cell allowing transport of needed materials in and out
consists of protein molecules imbedded in a lipid bilayer
2.
Vesicles – small membrane sacs pinched off of the cell membrane
store or transport materials in and out of the cell
3.
Cytoplasm – jelly-like cell contents
70% water with suspended organelles
4.
Nucleus – contains DNA, the genetic material of the cells (genes)
directs all cellular activities
materials leave the nucleus through nuclear pores in the nuclear membrane (or nuclear envelope)
5.
Nucleolus – region of the nucleus where ribosomes are produced
6.
Ribosomes – dense granules that may be found attached to rough ER or
free in the cytoplasm

are the site of protein synthesis – where amino acids are assembled into proteins according to the information stored in the DNA
7.
Endoplasmic reticulum (ER) – network of tubes branching from the
nucleus through which materials can be transported a) rough ER – has ribosomes on the surface b) smooth ER – has no ribosomes, produces and packages lipids
8.
Lysosomes – vesicles containing digestive enzymes
function to break down food particles, kill bacteria & destroy old or damaged cell parts
9.
Golgi apparatus – flat disc-shaped sacs that sort, modify & replace molecules sent from the ER; the needed materials are pinched off into vesicles and sent to other parts of the cell or to the cell membrane for transport out of the cell
lysosomes are produced here
10.
Mitochondria – rod-shaped organelle with folded inner membranes
site of cellular respiration in which chemical energy stored in sugars is converted into useable energy for the cell (ATP)

Cellular Respiration
C
6
H
12
O
6
+ 6O
2

6CO
2
+ 6H
2
O + energy
11.
Centrioles – cylindrical structures located just outside the nucleus of animal cells
- during cell division, centrioles help direct the separation of genetic material
12.
Vacuoles – balloon-like vesicles that store water, food, minerals, or wastes
animal vacuoles are smaller; plants usually have one large central vacuole
13.
Cell wall – rigid structure that protects and provides shape and support to plant, fungi & some bacterial cells
composed of cellulose, a complex carbohydrate (a.k.a. fibre or roughage in our diet)
14.
Chloroplasts – found only in green plants
contain stacks of flattened discs containing the green pigment chlorophyll
are the site of photosynthesis in which the Sun’s energy is converted into chemical energy (sugars)

Photosynthesis sunlight
6CO
2
+ 6H
2
O ----------- > C
6
H
12
O
6
+ 6O
2 chlorophyll
Do: p.284 Check Your Understanding
# 2, 3, 4, 6, 7, 8
Do: p.286 CH. 7 Review
# 4, 5, 7, 9, 11, 12, 15

Science Focus 10 Unit 3
8.1 Membrane Properties p. 290
The activities of a living cell depend on the ability of its
membrane to:
1.
transport raw materials into the cell (and out of)
2.
transport manufactured products and wastes out of the cell
3.
prevent unwanted matter from entering the cell
4.
prevent the escape of matter needed to perform cellular functions
Cell Membrane Structure
1.
phospholipid bilayer – each phospholipid molecule has a head that is hydrophilic (water-loving) and two tails that are hydrophobic (water-fearing)
2.
proteins – are embedded throughout the membrane serving the following functions: a) moving substances across the membrane b) carrying out chemical reactions (they act as enzymes)

c) some have “marker” molecules (carbohydrate chains) on their surface allowing cells to recognize each other d) allow messenger molecules (such as hormones) to attach e) assist in cell-to-cell communication and control of cell functions
Protein position within a membrane:
1.
Peripheral proteins – are partially embedded in the inside or outside surface of the membrane
2.
Integral proteins – extend through the entire bilayer and project from both surfaces
The Fluid-Mosaic Model
Cell membrane molecules are in constant motion (drifting past each other) resulting in: a) membrane flexibility b) cell’s ability to change shape
Do BLM 8-1 Cell Membranes
Cell Membrane Function
1.
A Biological Barrier
a cell membrane prevents many materials from entering the cell. Name 6:
- salts - atoms - viruses
- sugar
- proteins
- ions - bacteria

most organelles are surrounded by membranes with the same structure as a cell membrane
Apoptosis – when the lysosome bursts and releases it’s digestive enzymes into the cell, resulting in cell destruction
2.
A Selective Filter
Cell membranes are semi-permeable, allowing some materials to cross, while excluding others. They can select a) by particle size
small enough to enter membrane - O
2
, H
2
O
too large to cross - sugar b) particular materials to transport across (they bind to chemicals based on their size, shape or charge) p. 296 Cool Tools – Describe the freezefracture method and how it provided evidence for the fluid mosaic model.
[specimens are frozen in liquid nitrogen then cracked with a cold knife. The lipid bilayer can be separated, exposing the membrane proteins. Can coat with platinum
and examine with electron microscope]
Do Check Your Understanding p. 296 #1-6

Science Focus 10 Unit 3
8.2 Transport Across Cell Membranes
Selective Transport – the movement of only certain substances across the cell membrane
Particle Model of Matter – all matter is made of tiny particles
Brownian Motion – in a liquid or gas, particles are in constant, random motion p.297 Find Out Activity – Brownian Motion
Concentration Gradient – the difference in concentration between two areas for any given molecule produces a
gradient or path of movement in which molecules move toward areas where the concentration of particles is lower
- molecules move down a concentration gradient
Equilibrium – a state at which molecules are evenly distributed (the concentration is equal throughout the medium)
molecules continue moving but equilibrium is maintained
Types of Transport Across Membranes
A. Passive Transport – movement across cell membranes without an input of energy

Q. Name 2 reasons molecules move.
1. Brownian Motion
1. Concentration gradients
Three Types of Passive Transport
1.
Diffusion – the net movement of particles from an area of high concentration to an area of low concentration
no energy is expended
in a cell, very small particles can cross the cell membrane by moving between the phospholipid molecules
Q: Why does oxygen diffusing into the cell never reach equilibrium?
A: Your cells continually consume oxygen for cellular respiration, making the concentration inside always lower than the outside
Q: Describe the concentration gradient of carbon dioxide.
A: Higher concentrations in the cell so net movement is out of the cell.
Do BLM 8-3 Particle Model of Matter and Diffusion
Demo: p.298 The Amount of Water in Solutions

2.
Osmosis – the diffusion of water molecules across a membrane (water molecules move from where they are more highly concentrated to where they are less concentrated)
Solutions are described in terms of their concentration relative to another solution a) Hypotonic solution – has a lower concentration of solute compared to inside the cell
The solution is therefore more concentrated inside the cell and water will move into the cell. The cell will explode b) Hypertonic solution – has a higher concentration of solute compared to the inside of the cell
The solution is therefore less concentrated inside the cell and water will leave the cell. The cell will shrivel up c) Isotonic solution – has the same solute concentration on both sides of the cell membrane.
Equilibrium has been reached. EQUAL FLOW of water into and out of the cell
Q: a) What happens when a cell is placed into distilled water?
A: The cell is hypertonic and water moves into the cell & the cell may burst

Q: b) What is turgor pressure?
A: The cell wall of a plant resists the pressure of a water-filled vacuole keeping the plant firm
Q: c) What happens when a cell is placed into strong salt water?
A: The solution is hypertonic and water leaves the cell. The cell shrinks and may die (plasmolysis)
Q: d) What is plasmolysis?
A: Loss of water in a plant cell resulting in WILTING
Q: e) Why would drinking saltwater pose a problem?
A: Hypertonic solution outside cells would cause cells to lose water, shrink and die (dehydration)
Do BLM 8-4 Concentration Gradients
3.
Facilitated Diffusion – diffusion of molecules across the cell membrane by way of transport proteins.
- necessary for glucose, ions, and other substances that cannot cross the membrane by simple diffusion
Transport proteins have 3-D shapes that make them highly selective, recognizing atoms or molecules by shape, size or charge.

Two types of transport proteins: a) carrier proteins – facilitate the diffusion of glucose across the cell membrane
Q: Explain how glucose enters the cell.
A: Glucose fits into a groove on the carrier, the protein’s shape changes, and glucose is released on the inside of the cell b) channel proteins – have tunnel-like pores filled with water that allow charged ions in and out of the cell
B. Active Transport – the movement of molecules and ions against the concentration gradient which requires
ATP energy and carrier proteins to pump these molecules from an area of low solute concentration to an area of high solute concentration.
used to accumulate nutrients, or remove toxic materials or wastes
Most cells use 40% of their energy on active transport; kidney cells use
90% of their energy on using active transport to filter wastes out of your blood!

C. Bulk Transport – the use of vesicles to facilitate movement of substances that are too large to enter or exit the cell via transport proteins
Two types:
1.
ENDOCYTOSIS – the cell membrane forms a pocket around the material to be transported, then either pinches off as a vesicle or a vacuole.
Q: Differentiate between a vacuole & vesicle.
A: Vesicle transports contents; vacuole stores the ingested material
Two types of Endocytosis: a) phagocytosis - when cells “eat” by taking in large particles or other cells
Q: What happens after a new vesicle enters the cytoplasm of a cell?
A: It fuses with a lysosome and the enzymes would digest the material b) pinocytosis – when cells “drink” by taking in droplets of fluid
Receptor – mediated endocytosis – receptors, like antennae, detect specific compounds or cells and bind with them, triggering endocytosis.

Q: Give 2 examples of molecules entering by R.M.E.
A.
Cholesterol & HIV
2.
EXOCYTOSIS – the reverse of endocytosis, whereby the membrane of vesicles or vacuoles fuses with the cell membrane and the stored contents are expelled from the cell.
Q: Give 2 examples of expelled materials.
A: Wastes, enzymes, hormones
Do BLM 8-6 Types of Transport Across Cell Membranes
Do BLM 8-7 The Role of Cell Membranes in Endocytosis
and Exocytosis
Membranes at Work
1.
Water Purification
Reverse osmosis – uses pressure to force contaminated water through a membrane with fine pores that will not allow bacteria, salts, and other dissolved molecules through, resulting in water with fewer impurities
2.
Kidney Dialysis - filters toxic wastes that accumulate in the blood while retaining necessary proteins, glucose, amino acids & ions
- the patient’s blood is pumped through dialysis tubing, a synthetic, semi-permeable membrane. When

immersed into a salt solution, needed salts don’t diffuse, but wastes, which are hypertonic to the
dyalysate, diffuse out of the blood.
3.
Controlled Delivery of Medications – a) medication can be placed in a flat
transdermal patch that sticks to the skin. A semi-permeable membrane lining the inner surface allows drugs to diffuse out of the patch at a slow, constant rate.
Q: Give 4 examples of medications available in patches.
A: - nicotine (to quit smoking) - hormones for imbalances
- motion sickness drugs - contraceptive hormones
- pain reducers - weight-loss b) Liposomes – artificial vesicles that can safely transport medications from one part of the body to another
Two examples:

1) used to transport anti-cancer medications to tumours in cancer patients
2) liposomes, coated with the gene needed to cure cystic fibrosis, are sprayed into the patient’s nostrils
Do Check Your Understanding p.307 #2-
Do 8.2 Review Worksheet
Science Focus 10 Unit 3 8.3 Cell Size and Function
Particles entering the cell reach more to other areas of the cell by diffusion, due to a differing concentration gradient in the two areas.
Q. Compare rate of diffusion across a cell membrane with diffusion within a cell.
A. Concentration gradient within a cell is lower so diffusion in a cell is slow and inefficient.
Two reasons an amoeba could not function were it humansized:
1.
substances could diffuse through the cell membrane in less than a second, but would take more than a week to reach the centre of the cell.
2.
It would have a very low surface area – to – volume ratio making it difficult for adequate amounts of oxygen and nutrients to diffuse in

Q. What do scientists believe was the reason that the
Paleozoic Era could sustain the existance of giant insects?
A. The air was believed to be 35% oxygen
(now 21%) making the concentration gradient of oxygen much steeper and O
2 was able to efficiently move through longer tracheoles.
The
Do p.309 Charting Cell Size
Importance of Surface Area – to – Volume Ratio
***As a cell grows, volume increases faster than surface area.
Eg. If cell size is doubled, it would require eight times more nutrients and produce eight times more waste, but surface area would only have increased four times.
Result: 1. not enough surface area for oxygen,
nutrients, and waste exchange
2. cell would starve OR
3.
cell would be poisoned from a buildup of waste products
A cell with a surface area-to-volume ratio of 30:6 has to acquire 3 times the nutrients of a cell with a ratio of
10:2.
Q. Cell ratio of 18:6 requires ___ times the nutrients as a cell with a ratio of 3:1.

A. 6
The human body has more than 10 trillion cells. If 1000 average-sized cells were lined up, they would total less than 2 cm in length.
Cell Shape and Surface Area
Certain cell shapes increase surface area-to-volume ratio’s
Q.
Complete the chart with two types of cells whose shape produces a large surface area.
Name of Cell Sketch Function of Cell
1.
2.
From One Cell to Many Cells
How do some organisms function at enormous sizes?
A.
They are multicellular and grow by adding more cells instead of simply growing larger cells,
Result: Rapid diffusion within cells exists
Cell Specialization – in multicellular organisms, cells are organized into tissues that do specific jobs.
Q.
Give an example of cell specialization in your
body.
A.
- lungs – gas exchange

- heart & blood vessels – transport of O
2
, nutrients &
wastes
- kidneys – water regulation and excretion of wastes
- digestive system – nutrient digestion and absorption
- etc.
Do p.314 Check Your Understanding Q. 1 – 7
Science Focus 10 Unit 3 p.318
Chapter 9: From Cell to Organism:
Focus on Plants
9.1
Specialized and Organized
Q. What functions need to be carried out by the leaf of a plant?
A. gas exchange release water protect leaf cells leaf photosynthesis transport water & nutrients through
In single-celled organisms, one cell performs all the functions of life.
In multi-cellular organisms, groups of similar cells (called tissues) are specialized to perform specific tasks.
Q. Name 4 specialized cells in the human body.
A. cells of the intestinal lining
muscle cells nerve cells skin cells
Cell Specialization in Leaves
Photosynthesis occurs in the chloroplasts of plant cells

6CO
2(g)
+ 6H
2
O
(l)
light
----------- C
6 chlorophyll
H
12
O
6(s)
+ 6O
Cellular respiration occurs in the mitochondria of plant and animal cells.
C
6
H
12
O
6(s)
+ 6O
2(g)
-------- 6CO
2(g)
+ 6H
2
O
(l)
2(g)
Cells of the Leaf
Do BLM 9-1 Photosynthesis and Respiration in Plants
1.
Epidermal Cells – make up the epidermis a) Description - flat, single cell layer covering the upper and lower surfaces of the leaf
- transparent, which allows solar energy to pass through to cells beneath
- a waxy cuticle coats the cells to prevent evaporation of water b) Function – to protect the leaf, therefore do not contain chloroplasts
2.
Palisade Tissue Cells a) Description – long and narrow (columnar) cells packed closely together lying just below the epidermis b) Function – major photosynthesis, therefore packed with chloroplasts
3.
Spongy Tissue Cells a) Description – round, loosely packed cells found just below palisade layer; contain chloroplasts b) Function – gas and water exchange, minor photosynthesis

4.
Stomata and Guard Cells a) Description – stomata (singular-stoma) are tiny openings on the underside of a leaf
- each stoma is controlled by 2 guard cells b) Function – stomata allow exchange of carbon dioxide, oxygen and water vapor
5.
Vascular Tissue Cells a) Description – a series of tubes or leaf veins called phloem and xylem, which are arranged together in vascular bundles b) Function –
XYLEM – carries water and minerals from roots to leaves
PHLOEM – carries sugars made by the leaves to other parts of the plant

Q.
Do an analogy of leaf tissues and human body tissues
A.
skin = epidermis; circulation system = vascular tissue; lungs = stomata
Do BLM 9-2 Cell Specialization in Leaves
Do F.O. Activity Turn Over a New Leaf p. 322
Cell, Tissue, Organ, System
Q.
Name 3 advantages multicellular organisms have
over single-celled organisms.
A.
– larger size
- a variety of specialized cells
- an ability to thrive in a broader range of environments
Multicellularity, however, requires a high degree of organization of the numerous cells in order to perform their functions efficiently. (The human body contains approx. 100 trillion cells.)
Levels of Organization
Cells – basic unit of organization eg. Human – stomach cell
Plant - phloem cell
Tissues – many cells with the same structure and functions clustered together eg. Human – muscle tissue of stomach

Plant – epidermal tissue
Organs – multiple tissues working together to perform a specific function eg. Human – stomach
Plant – leaf
Systems – organs working together to perform a complex function eg. Human – digestive system
Plant – vascular system
Science Focus 10 Unit 3 9.2 Gas Exchange in Plants
During cellular respiration in animal and plant cells, exhaled air contains lower O
2
levels and higher CO
2
level than inhaled air.
During photosynthesis, plants consume CO
2
and H
2
O and produce
O
2
.
Leaves and Lenticles
Leaves
Gases diffuse into stomata of plant leaves and move through air spaces between the spongy and palisade tissue cells. CO
2
dissolves into the watery film around the cells and diffuses into the cells of the leaf where chloroplasts use the CO
2
for photosynthesis. O
2
produced diffuses out of the leaf cells and leaves through the stomata.
Roots and Stems
- some gas exchange occurs in surface cells

- in woody plants, layers of dead cork cells and waxy substances prevent gas exchange
- Lenticels, which appear as slashes on stems of trees and herbaceous plants, are natural pores through which gas exchange can occur.
Investigation 9-A Carbon Dioxide Consumption by Cabomba p.326
Gas Exchange Is Tied to Water Loss
Q. How do plants carry out evaporative cooling?
A. By transpiration.
Q. How can this process function as a survival mechanism for plants?
A. Can cool leaf 10-15  C and prevent heat damage.
Transpiration is the evaporation of water from leaves of plants. This can be as much as
99% of the water absorbed by the roots.
TRIVIA: A single corn plant can lose between 135 L and
200 L of water through transpiration in one growing season.
Transpiration and gas exchange are controlled by the shape of guard cells which open stomata to allow CO
2
H
2
in and O
2
and
O out. More photosynthesis occurs when stomata are open.
OPENED STOMATA – occurs when high water pressure, called turgor pressure, causes water to move into the guard cells by osmosis. The guard cells swell and the stomata open, allowing

transpiration. (Occurs most during the day). (Or on: Sunny days, humid days, warm temperatures)
CLOSED STOMATA – occurs when the amount of water in the guard cells decreases and they shrink and the stomata close.
(Occurs most during the night, except in desert plants where stomata only open at night due to dry conditions).
WILTED PLANTS – result from reduced turgor pressure as a result of water loss. p.330 Find Out Activity Open and Shut
Do BLM 9-3 Gas and Water Movement In Leaves
Do Check Your Understanding p.330 #1-4

Science Focus 10 Unit C 9.3 Water Transport in Plants p.331
Xylem Vessels and Phloem Vessels
Xylem and phloem make up the vascular tissue of plants, transporting water, minerals, and sugars through a series of interconnected tubes through the leaves, stems and roots.
XYLEM – transports water and dissolved minerals from soil to
leaves.
in mature plants, most xylem cells are dead, only cell walls remain, forming hollow tubes called xylem vessels.
Detailed Structure of Xylem Vessels – consists of long hollow cells called tracheids or vessel elements, which are joined by small pits, allowing water to flow through.
PHLOEM – transports sugars produced during photosynthesis
from leaves to roots. Cylindrical cells joined end to
end form phloem vessels, which are living cells with
porous cell walls. Sugary sap flows down the phloem vessels and passes through these pores.
Detailed Structure of Phloem Vessels – consists of sieve tubes, cylindrical cells joined by a sieve plate. A companion cell lies alongside each sieve tube cell, offering support because the sieve tube cell lacks many organelles.
Water Uptake in Roots
Roots are covered with epidermal tissue which is permeable to water only at the root tip. Water enters the root tips by osmosis until it reaches the xylem.

Root hairs – increase surface area for absorbing water & dissolved minerals.
are each an outgrowth of a single epidermal cell
WOW! The total surface area of a plant’s roots may be
up to 50X greater than the surface area of its leaves
- minerals enter the root by facilitated diffusion or active transport
- the solution of water & minerals in root xylem is called xylem sap.
- xylem carries the xylem sap up to stems & leaves (branching into leaf veins) eventually being absorbed by all cells of the plant
Properties of Water
Two properties of water allow xylem sap to rise great distances against gravity
1.
Cohesion – the attraction of water molecules to other water molecules due to their polar nature. (Observed as water forms droplets)

- the column of xylem sap can be broken by a break in the vessel or a bubble in the sap.
Q: Explain how each of these situations could be caused.
A: Break – cut in root, stem or leaf
Bubble – freezing in winter
2.
Adhesion – the attraction of water molecules to molecules of other substances. (Observed as water sticks to the glass in a graduated cylinder, forms a meniscus)
- water also clings to the cellulose wall of a xylem vessel, preventing the sap from falling back towards the roots, thus helping to fight the force of gravity.
The two main mechanisms that aid the upward movement of water in plants are root pressure and transpiration.
A. Root Pressure Pushes
Root pressure occurs when root cells actively transport minerals into the xylem. This causes water to diffuse into this hypertonic area, building root

pressure in the xylem which forces fluid up the xylem vessels.
Fluid seeping from a cut stem of a plant occurs due to root pressure.
Q: Will all transport cease due to a cut halfway up the stem?
A: Xylem sap will still flow upwards above the cut (compare to a cut straw)
DEMO p.335 Up With Root Pressure
B. Transpiration Pulls
Transpiration of water from leaf stomata generates a pulling force, aiding the upward transport of water –
1.
The energy for xylem transport ultimately comes from the heat of the Sun.
2.
Water molecules evaporate leaving the air within the leaf slightly drier
3.
Water then diffuses out of leaf cells into intracellular fluid where solutes are more concentrated
4.
As evaporation from the leaf continues, the cohesion of water molecules draws the water up the xylem vessels, replacing evaporated water.
Adhesion of water molecules to the walls of xylem vessels aids the process.

Transpiration increases as temperature rises, increasing water movement through xylem. Xylem transport speed can be up to 50 meters/hour
Do BLM 9-4 Transpiration Rate in Plants
Sugar Transport in Phloem
Sugars produced by the palisade and spongy tissue cells of the leaf are transported to the stems and roots by phloem vessels
1.
Sugar, minerals, and other nutrients enter phloem by active transport
2.
Water flows by osmosis, causing phloem cells to swell with turgor pressure. ( Sugar + nutrients + water = phloem sap)
3.
Phloem sap flows down the concentration gradient and the fluid pressure forces the sap through pores in phloem cell walls and into surrounding cells
4.
The nutrients are continually used up by tissues of the stem and root resulting in a pressure gradient that causes a continual flow of solution from leaf to root.
Phloem transport ranges from 20 cm/hr to 100 cm/hr
Q: How do aphids help researchers study phloem?
A: After they probe a phloem cell with their stylet, researchers cut off the stylet. Phloem continues to ooze out and can be studied. NOTE: – artificial probes injure the phloem cells.
Do p.339 Investigation “The Flow in Phloem”
Do p.340 Check Your Understanding Questions 1-7

Science Focus 10 Unit 3 9.4 Plant Control Systems
Tropisms are plant responses in which the plant grows towards or away from a stimulus (=an environmental factor, ex. Light, gravity, touch)
1.
Phototropism is the growth of a plant toward a light source.
WHY? This maximizes light absorption for photosynthesis which fuels plant growth
HOW? Plant cells respond to light by growing at different rates. When cells on one side of a stem grow more elongated than cells on the other side, the stem curves.
SKETCH AND LABEL a plant bending towards the Sun, indicating area of elongation.
(See p.341 Fig. 9.18)
Do p.342 The Darwins Experiment

THE MECHANISM
Charles and Francis Darwin concluded that the tip of the seedling detects light, transmits that information to the stem, and the rate of growth of stem cells is affected. The
Darwins suspected a chemical signal triggered the growth.
Decades later, Peter Boysen-Jensen tested the presence of a chemical signal, finding that the chemical could pass through gelatin but not mica. (See Fig. 9.19, p.344)
THE HORMONE
In 1926, Frit Went confirmed that a chemical he named
“auxin” (meaning to grow”) was produced in the plant tip.
Auxin is actively transported through the cells towards the shaded side of the stem causing cells there to grow longer than cells on the lighted side, resulting in bending towards the light.
Q: Summarize Went’s experiment on p.345, Fig. 9.20
A: Agar containing auxin caused cell elongation in stems on which ever side it was placed (light not being a factor)
2.
Gravitropism – is the growth of a plant in response to the force of gravity
1.
Negative gravitropism – stem grows towards sunlight and against the force of gravity
2.
Positive gravitropism – roots grow into the soil & towards the force of gravity
THE MECHANISM
Gravitropism occurs as soon as seeds germinate and the response of the stems and roots is consistent regardless of how the seed is oriented when it is planted.

Auxin is responsible for the plant growth response to gravity. a) IN THE STEM – when a plant is placed on its side, more auxin collects in the cells on the stems lower side. These cells then grow longer resulting in the stem curving upward. b) IN THE ROOT – increased auxin concentration inhibits root growth. When a root is placed sideways, auxin collects along the lower side but cell growth is inhibited here. Cells on the upper side, however, continue to grow longer, resulting in the root growing downward.
Another theory of positive gravitropism is that dense starch grains in the root tip cells may settle at the low point in cells signalling the direction of gravity and influencing the direction of growth.
DO p.346 Spinning Seeds
3. Nastic Response is a plant’s response to touch. The stimulus of touch sends an electrical signal to certain leaf cells resulting in a drop in turgor pressure. This causes the leaf to collapse.
Q: Give two examples of plants exhibiting a nastic response
(See p.344)
A: Mimosa, Venus Fly Trap
4. Thigmotropism is a rapid growth of certain plant cells in response to touch. It is seen in plants that use tendrils to wrap around supports or other plant stems. Eg. The tendrils of a pea plant that come in contact with a chain-link fence will wrap around it, gaining support as it grows.
Do BLM 9-6 Discovering Tropisms
Do 9.4 Review: p.348 Q. 1-7
Do Chapter 9 Review p.350 Q. 1-8, 10, 11