Stomata

Guard Cells and Stomata

Stomata are gaps in the lower epidermis of leaves that facilitate (make easier) the diffusion of gases, including evaporated water, in and out of the leaf. Guard cells can open and close the stomata:

Opening the stomata

The guard cells can open the stomata by taking up lots of water, causing them to swell.

Closing the stomata

To close the stomata, the guard cells lose water and return to a limp state.

State of Stomata

The state of stomata (open or closed) achieves a balance between allowing gases for photosynthesis into the leaves, and conserving water in the plant.

Abundant water

When water is abundant (lots available) the plant can afford to lose water.
So it opens the stomata to allow gases for photosynthesis to move freely in and out of the leaf.

Scarce water

When water is scarce (rare), stomata close in order to prevent further water loss.
- This is achieved by guard cells returning to a limp state after they lose water.

Time of day

At night, stomata close because, in the absence of sunlight, carbon dioxide is not required for photosynthesis.
- At this time, their only objective is to prevent water loss.

1Cell Biology

1.1What's in Cells?

1.1.1Types of Cells

1.1.2Properties of Prokaryotes

1.1.3Standard Form

1.1.4Standard Form - Calculations

1.1.5Addition in Standard Form - Calculations

1.1.6Subtraction in Standard Form - Calculations

1.1.7Multiplication in Standard Form - Calculations

1.1.8Division in Standard Form - Calculations

1.1.9Animal Cells

1.1.10Plant Cells

1.1.11Differences Between Animal & Plant Cells

1.1.12Bacterial Cells

1.1.13Types of Cells HyperLearning

1.1.14Cell Specialisation in Animals

1.1.15Sperm Cells

1.1.16Nerve Cells

1.1.17Muscle Cells

1.1.18Cell Specialisation in Plants

1.1.19Microscopy

1.1.20Developments in Microscopy

1.1.21Microscope Practical

1.1.22Microscopy - Calculations

1.1.23Culturing Microorganisms

1.1.24Contamination

1.1.25Avoiding Contamination

1.1.26Calculating Bacteria

1.1.27Calculating Bacteria - Calculations

1.1.28End of Topic Test - What's in Cells?

1.1.29Exam-Style Questions - Cell Structure & Microscopy

1.2Cell Division

1.2.1Chromosomes

1.2.2The Cell Cycle

1.2.3Mitosis

1.2.4Exam-Style Questions - Mitosis & Cell Cycle

1.2.5Stem Cells

1.2.6Use of Stem Cells

1.2.7Disadvantages of Stem Cells

1.3Transport in Cells

1.3.1Diffusion

1.3.2Factors Affecting Diffusion

1.3.3Surface Area : Volume

1.3.4Surface Area : Volume - Calculations

1.3.5Exchange Surfaces

1.3.6Examples of Exchange Surfaces

1.3.7Osmosis

1.3.8Osmosis Practical

1.3.9Active Transport

1.3.10Transport in Cells

1.3.11End of Topic Test - Cell Division & Transport

1.3.12Grade 9 - Cell Transport

2Organisation

2.1Principles of Organisation

2.1.1Cells & Tissues

2.1.2Organs

2.1.3Organ Systems

2.1.4Organisms

2.2Enzymes

2.2.1Enzymes

2.2.2Enzymes HyperFlashcards

2.2.3Rate of Reaction

2.2.4Calculating Rate of Reaction

2.2.5Rate of Reaction - Calculations

2.2.6Digestion

2.2.7Bile

2.2.8Examples of Digestive Enzymes - Amylase

2.2.9Examples of Digestive Enzymes - Protease

2.2.10Examples of Digestive Enzymes - Lipase

2.2.11Testing for Biological Molecules

2.2.12End of Topic Test - Organisation & Enzymes

2.2.13Grade 9 - Enzymes

2.2.14Exam-Style Questions - Enzymes

2.3Circulatory System

2.3.1Types of Blood Vessel

2.3.2Blood Vessels - Arteries

2.3.3Blood Vessels - Capillaries

2.3.4Blood Vessels - Veins

2.3.5The Heart - Structure

2.3.6The Heart - Function

2.3.7Important Blood Vessels

2.3.8Double Circulatory System

2.3.9Gas Exchange

2.3.10Gas exchange - Calculations

2.3.11Alveoli

2.3.12Blood Components

2.3.13Platelets

2.3.14Red Blood Cells

2.3.15White Blood Cells

2.3.16End of Topic Test - Circulatory System

2.4Non-Communicable Diseases

2.4.1Health Issues

2.4.2Disease Interactions

2.4.3Sampling

2.4.4Sampling - Calculations

2.4.5Risk Factors

2.4.6Examples of Risk Factors

2.4.7Risk Factor Graphs

2.4.8Coronary Heart Disease

2.4.9Heart Valve Disease

2.4.10Heart Failure

2.4.11Treating Heart Disease

2.4.12Cancer

2.4.13Cancer Risk Factors

2.4.14End of Topic Test - Non-Communicable Diseases

2.4.15Exam-Style Questions - Coronary Heart Disease

2.5Plant Tissues, Organs & Systems

2.5.1Plant Tissues

2.5.2Leaves

2.5.3Transpiration

2.5.4Rate of Transpiration

2.5.5Measuring Transpiration

2.5.6Translocation

2.5.7Transpiration Tissues

2.5.8Stomata

2.5.9Premium Knowledge - Transpiration

2.5.10End of Topic Test - Plants

2.5.11Exam-Style Questions - Plant Tissues

3Infection & Response

3.1Communicable Disease

3.1.1Spreading Disease

3.1.2Viruses

3.1.3Other Pathogens

3.1.4Human Defence Systems

3.1.5Human Defence Systems 2

3.1.6Grade 9 - Immune System

3.1.7Antibiotics

3.1.8Drug Development

3.1.9Drug Testing

3.1.10Drug Testing / Efficacy - Calculations

3.1.11End of Topic Test - Communicable Diseases

3.1.12Exam-Style Questions - Microorganisms & Disease

3.2Monoclonal Antibodies

3.2.1Producing & Using Monoclonal Antibodies

3.2.2Grade 9 - Monoclonal Antibodies

3.3Plant Diseases

3.3.1Diseases & Defence

3.3.2Identifying Disease

3.3.3End of Topic Test - Antibodies & Plant Disease

4Bioenergetics

4.1Photosynthesis

4.1.1Photosynthesis

4.1.2Photosynthesis 2

4.1.3Photosynthesis - Calculations

4.1.4Photosynthesis Experiments

4.1.5Grade 9 - Photosynthesis Experiment

4.1.6Exam-Style Questions - Rate of Photosynthesis

4.2Respiration

4.2.1Respiration

4.2.2Respiration - Calculations

4.2.3Exercise

4.2.4Respiration HyperLearning

4.2.5End of Topic Test - Photosynthesis and Respiration

4.2.6Exam-Style Questions - Anaerobic Respiration

5Homeostasis & Response

5.1Homeostasis

5.1.1Homeostasis

5.1.2Homeostasis & Negative Feedback

5.1.3Exam-Style Questions - Exercise & Homeostasis

5.2The Human Nervous System

5.2.1The Nervous System

5.2.2The Nervous System HyperFlashcards

5.2.3Synapses

5.2.4Reflexes

5.2.5Exam-Style Questions - Nervous System

5.2.6The Brain

5.2.7Eye Anatomy

5.2.8Eye Function

5.2.9Control of Body Temperature

5.2.10Warming Up & Cooling Down

5.2.11Body Temperature HyperLearning

5.2.12End of Topic Test - Human Nervous System

5.3Hormonal Coordination in Humans

5.3.1Endocrine System

5.3.2Thyroxine & Adrenaline

5.3.3Blood Glucose

5.3.4Diabetes

5.3.5Control of Water Balance

5.3.6Urine

5.3.7Dialysis

5.3.8Transplants

5.3.9Puberty

5.3.10Menstruation

5.3.11Contraception

5.3.12Contraception 2

5.3.13Hormones for Infertility

5.3.14End of Topic Test - Homeostasis & Hormones

5.3.15Grade 9 - Hormonal Coordination

5.3.16Exam-Style Questions - Hormones & Contraception

5.4Plant Hormones

5.4.1Plant Hormones

5.4.2Plant Hormones 2

5.4.3End of Topic Test - Hormones

6Inheritance, Variation & Evolution

6.1Reproduction

6.1.1Reproduction

6.1.2Reproduction 2

6.1.3Genome

6.1.4DNA

6.1.5Protein Synthesis

6.1.6Genetic Inheritance

6.1.7Genetic Crosses

6.1.8Inherited Disorders

6.1.9Inherited Disorders 2

6.1.10Genetic Crosses - Calculations

6.1.11Genome Screening & Sex Determination

6.1.12End of Topic Test - Reproduction

6.1.13Exam-Style Questions - DNA & Genetics

6.2Variation & Evolution

6.2.1Variation & Evolution

6.2.2Selective Breeding

6.2.3Selective Breeding 2

6.2.4Genetic Engineering

6.2.5Uses of Genetic Modification

6.2.6Cloning

6.2.7Cloning 2

6.2.8End of Topic Test - Variation & Evolution

6.2.9Exam-Style Questions - Selective Breeding

6.3Genetics & Evolution

6.3.1Natural Selection

6.3.2Speciation

6.3.3Evidence for Evolution

6.3.4Genetics & Extinction

6.3.5Grade 9 - Evolution

6.4Classification

6.4.1Classification of Living Organisms

6.4.2Classification of Living Organisms 2

6.4.3End of Topic - Genetics & Classification

7Ecology

7.1Adaptations & Interdependence

7.1.1Communities

7.1.2Communities 2

7.2Organisation of Ecosystems

7.2.1Population Dynamics

7.2.2Environmental Change

7.2.3Assessing Ecosystems

7.2.4Assessing Ecosystems - Calculations

7.2.5The Cycling of Materials

7.2.6Decay

7.2.7Decay Practical

7.2.8End of Topic Test - Organisation of Ecosystems

7.2.9Grade 9 - Ecosystems

7.2.10Exam-Style Questions - Decomposition

7.3Biodiversity

7.3.1Human Interactions with Ecosystems

7.3.2Human Interactions with Ecosystems 2

7.3.3Greenhouse Gases

7.3.4Greenhouse Gases 2

7.3.5Hardest Questions - Humans & the Environment

7.3.6End of Topic Test - Adaptations & Biodiversity

7.4Trophic Levels

7.4.1Trophic Levels

7.4.2Trophic Levels 2

7.4.3Transfer efficiency - Calculations

7.4.4Premium Knowledge - Trophic Levels & Food Chains

7.4.5Exam-Style Questions - Food Chains

7.5Food Production

7.5.1Food Production

7.5.2Farming & Fishing

7.5.3Food Production - Calculations

7.5.4End of Topic Test - Food & Trophic Levels

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