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.2587.1 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 mudb)rats came from garbage or dirty laundryc) maggots came from rotting materiald) mice came from a pile of wheat huskse) 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.259Jar 1: meat, left uncovered -> maggots appeared

Jar 2: meat, covered in cloth -> no maggots appeared

Maggots appeared in Jar 1 because _____________ ________________________.

C.Louis Pasteur (1822 – 1895) – French scientist who finally settled the continued debate of the theory of abiogenesis.

Pasteur’s experiment:

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 micro-organisms.

a)a swan-neck glass flask (figure 7.3) full of nutrient-rich 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: ________________ _______________________________________

Discovering Cells

As a result: The accepted theory became biogenesis – living things could only arise from other living organisms (suggested by Vichow in 1858)

Prior to seeing bacteria, the common assumption was that curses or supernatural spirits caused diseases!

< --------- airborne _________ settled here

*WORD Biogenesis - Latin root “bio” = of living CONNECT things and “genesis” =

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

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

A.Robert Hooke (1635 – 1703) – looked at cork with a compound light microscope (30X magnification) and was the first to see and name “cells”.

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!

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)

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.

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 p. 2667.2 Cells and Technology

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

The Cell Theory1. 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.

- magnifies up to 1.2 million timeselectron 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 projectto sequence all 30,000 to 40,000 human genes

- sequence information can be used to diagnose and treat genetic disorderseg. gene therapy – human gene is “corrected” to help cure a disorder or cancer

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

Demo: Extract DNA from pea soup

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

treatmentsd) 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 & energyb)convert energy (eg. photosynthesis)c) construct & maintain the molecules making up

the cell structured)carry out chemical reactionse)eliminate wastesf) reproducing

Organelles – internal cell parts that carry out specific functions

Prokaryotes – one-celled organisms lacking a membrane-bound 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 membrane-bound nucleus & organelles

- eg. most plant and animal cells

Cell Organelles

1. Cell membrane (plasma membrane)- a protective barrier for the cell allowing

transport of needed materials in and out

In Latin: “karyon” means nucleus“pro” means before“eu” means true

therefore: prokaryote means before nucleus. eukaryote means true nucleus.

- 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)

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

Cellular Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + energy

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)

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

Photosynthesis

sunlight 6CO2 + 6H2O ----------- > C6H12O6 + 6O2

chlorophyll

Science Focus 10 Unit 3 p. 290 8.1 Membrane Properties

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 cell3. prevent unwanted matter from entering the cell4. 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 membraneb)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 membrane2. Integral proteins – extend through the entire

bilayer and project from both surfaces

The Fluid-Mosaic ModelCell membrane molecules are in constant motion (drifting past each other) resulting in:a)membrane flexibilityb)cell’s ability to change shape

Cell Membrane Function1.A Biological Barrier

- a cell membrane prevents many materials from entering the cell. Name 6:- salts - atoms - viruses- sugar - ions - bacteria- proteins

Do BLM 8-1 Cell Membranes

- 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 FilterCell membranes are semi-permeable, allowing

some materials to cross, while excluding others. They can select

a)by particle size- small enough to enter membrane - O2, H2O- 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 freeze-fracture 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

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 Motion1. Concentration gradients

p.297 Find Out Activity – Brownian Motion

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.

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

Do BLM 8-3 Particle Model of Matter and Diffusion

Demo: p.298 The Amount of Water in Solutions

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)

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

Do BLM 8-4 Concentration Gradients

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

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

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!

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

Membranes at Work

1.Water PurificationReverse osmosis – uses pressure to force contaminated water through a membrane with fine pores that will not allow bacteria, salts, and other

Do BLM 8-6 Types of Transport Across Cell Membranes

Do BLM 8-7 The Role of Cell Membranes in Endocytosis

and Exocytosis

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 patients2) 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 human-sized: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 O2 was able to efficiently move through longer tracheoles.

The 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 exchange2. cell would starve OR3. 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.

Do p.309 Charting Cell Size

Q. Cell ratio of 18:6 requires ___ times the nutrients as a cell with a ratio of 3:1.A. 6

Cell Shape and Surface Area

Certain cell shapes increase surface area-to-volume ratio’sQ. Complete the chart with two types of cells whose shape produces a large surface area.

Name of Cell Sketch Function of Cell1.

2.

From One Cell to Many CellsHow 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 O2, nutrients &

wastes

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.

- kidneys – water regulation and excretion of wastes

- digestive system – nutrient digestion and absorption- etc.

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 waterprotect leaf cellsphotosynthesistransport water & nutrients through

leaf

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 nerve cells muscle cells skin cells

Cell Specialization in Leaves

Photosynthesis occurs in the chloroplasts of plant cells light

6CO2(g) + 6H2O(l) ------------ C6H12O6(s) + 6O2(g)chlorophyll

Do p.314 Check Your Understanding Q. 1 – 7

Cellular respiration occurs in the mitochondria of plant and animal cells.

C6H12O6(s) + 6O2(g) --------- 6CO2(g) + 6H2O(l)Cells of the Leaf

1.E

pidermal Cells – make up the epidermisa) 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 Cellsa) Description – long and narrow (columnar) cells

packed closely together lying just below the epidermisb) Function – major photosynthesis, therefore packed

with chloroplasts

3. Spongy Tissue Cellsa) Description – round, loosely packed cells found just

below palisade layer; contain chloroplastsb) Function – gas and water exchange, minor

photosynthesis

4. Stomata and Guard Cellsa) Description – stomata (singular-

stoma) are tiny openings on the underside of a leaf- each stoma is controlled by 2 guard cells

Do BLM 9-1 Photosynthesis and Respiration in Plants

b) Function – stomata allow exchange of carbon dioxide, oxygen and water vapor

5. Vascular Tissue Cellsa) 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

leavesPHLOEM – 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

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

Do BLM 9-2 Cell Specialization in Leaves

Do F.O. Activity Turn Over a New Leaf p. 322

eg. Human – stomachPlant – leaf

Systems – organs working together to perform a complex function

eg. Human – digestive systemPlant – 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 O2 levels and higher CO2 level than inhaled air.

During photosynthesis, plants consume CO2 and H2O and produce O2.

Leaves and Lenticles

Leaves

Gases diffuse into stomata of plant leaves and move through air spaces between the spongy and palisade tissue cells. CO2 dissolves into the watery film around the cells and diffuses into the cells of the leaf where chloroplasts use the CO2 for photosynthesis. O2 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 10-15C 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.

Transpiration and gas exchange are controlled by the shape of guard cells which open stomata to allow CO2 in and O2 and H2O 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.

TRIVIA: A single corn plant can lose between 135 L and 200 L of water through transpiration in one growing season.

Do Check Your Understanding p.330 #1-4

Science Focus 10 Unit C 9.3 Water Transport in Plantsp.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.

p.330 Find Out Activity Open and Shut

Do BLM 9-3 Gas and Water Movement In Leaves

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 RootsRoots 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

- 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

WOW! The total surface area of a plant’s roots may be up to 50X greater than the surface area of its leaves

Properties of WaterTwo 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 PushesRoot 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)

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.

DEMO p.335 Up With Root Pressure

Adhesion of water molecules to the walls of xylem vessels aids the process.

Do BLM 9-4 Transpiration Rate in Plants

Sugar Transport in PhloemSugars produced by the palisade and spongy tissue cells of the leaf are transported to the stems and roots by phloem vessels1. Sugar, minerals, and other nutrients enter phloem by

active transport2. 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.

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

Transpiration increases as temperature rises, increasing water movement through xylem. Xylem transport speed can be up to 50 meters/hour

Phloem transport ranges from 20 cm/hr to 100 cm/hr

ooze out and can be studied. NOTE: – artificial probes injure the phloem cells.

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.339 Investigation “The Flow in Phloem”

Do p.340 Check Your Understanding Questions 1-7

THE MECHANISMCharles 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 HORMONEIn 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. 9.20A: 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

Do p.342 The Darwins Experiment

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.

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

DO p.346 Spinning Seeds