Stomata

Guard Cells and Stomata

Stomata are pores 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, swelling and becoming turgid.
Guard cells will open the stomata when:
- There is the presence of light, for photosynthesis.
- There is high humidity, which reduces water loss, allowing stomata to remain open.

Closing the stomata

To close the stomata, the guard cells lose water and return to a flaccid state.
Guard cells will close the stomata when:
- It is dark, as photosynthesis slows, and stomata close to conserve water.
- There is low water availability, to reduce water loss.
- There are high temperatures to prevent evaporation and preserve water.

Gases

Carbon dioxide (CO₂): Enters the plant for photosynthesis.
Oxygen (O₂): Leaves the plant as a byproduct of photosynthesis.
Water vapour: Also moves out during transpiration.

1Classification of Living Organisms

1.1Characteristics of Living Organisms

1.1.1MRS GREN

1.1.2M.R.S.

1.1.3G.R.E.N.

1.2Concept and Uses of Classification Systems

1.2.1Classification

1.2.2Linnaean Classification

1.2.3Evolutionary Trees

1.2.4Ancestors & DNA

1.3Features of Organisms

1.3.1Dichotomous Keys

1.3.2Kingdoms - Animals & Plants

1.3.3Other Kingdoms

1.3.4Vertebrates

1.3.5Anthropods

1.3.6Plant Classification

1.3.7Cellular Structures - Cells

1.3.8Cellular Structures - Viruses

2Organisation of the Organism

3Movement Into & Out of Cells

3.1Diffusion

3.1.1Diffusion

3.1.2Factors Affecting Diffusion

3.1.3Surface Area : Volume

3.2Osmosis

3.2.1Osmosis

3.2.2Osmosis Experiment

3.2.3Osmosis in Plants

3.2.4Osmotic Balance

3.2.5Required Practical - Osmosis

3.3Active Transport

3.3.1Active Transport

3.3.2Transport in Cells

3.3.3Carrier Proteins

3.3.4Grade 9 - Cell Transport

3.3.5End of Topic Test - Cell Transport

3.3.6Exam-Style Questions - Substance Exchange

4Biological Molecules

4.1Biological Molecules

4.1.1Chemical Elements

4.1.2Larger Molecules

4.1.3Water

4.1.4Testing for Biological Molecules

4.1.5DNA

4.1.6DNA Pairings

5Enzymes

5.1Enzymes

5.1.1Enzymes

5.1.2Rate of Enzyme Action

5.1.3Investigating Rate

5.1.4Rate of Reaction - Calculations

5.1.5End of Topic Test - Enzymes

5.1.6Grade 9 - Enzymes

6Plant Nutrition

6.1Photosynthesis

6.1.1Photosynthesis

6.1.2Photosynthesis - Plant Gas Exchange

6.1.3Photosynthesis in Farming

6.1.4Uses of Glucose

6.1.5Ion Deficiency Conditions

6.1.6Rate of Photosynthesis

6.1.7Photosynthesis Experiments

6.1.8Photosynthesis Equation

6.1.9Photosynthesis - Calculations

6.1.10Limiting Factors

6.1.11Grade 9 - Photosynthesis Experiment

6.1.12Exam-Style Questions - Photosynthesis

6.2Leaf Structure

6.2.1Leaf Structure

6.2.2Stomata

6.2.3States of Stomata

6.2.4Plant Tissues

6.2.5Leaf Adaptations

6.2.6End of Topic Test - Photosynthesis

7Human Nutrition

7.1Diet

7.1.1Diet

7.1.2Vitamins & Minerals

7.1.3Dietary Needs

7.2Digestive System

7.2.1Digestive System

7.2.2Steps of Digestion

7.2.3Diarrhoea

7.3Physical Digestion

7.3.1Physical Digestion - Human Tooth

7.3.2Teeth Types

7.3.3Tooth Diseases

7.4Chemical Digestion

7.4.1Digestive Enzymes

7.4.2Examples of Digestive Enzymes - Amylases

7.4.3Examples of Digestive Enzymes - Proteases

7.4.4Examples of Digestive Enzymes - Lipases

7.4.5Chemical Digestion - Stomach

7.4.6Exam-Style Questions - Digestive Enzymes

7.4.7Pepsin & Trypsin

7.5Absorption

7.5.1Small Intestine

7.5.2Villi

8Transport in Plants

8.1Xylem & Phloem

8.1.1Plant Vessels

8.1.2Specialised Plant Cells - Xylem

8.2Water Uptake

8.2.1Water Uptake

8.2.2Specialised Plant Cells - Root Hair

8.2.3Exam-Style Questions - Transport in Plants

8.3Transpiration

8.3.1Transpiration

8.3.2Transpiration Tissues - Xylem

8.3.3Rate of Transpiration

8.3.4Measuring Transpiration

8.4Translocation

8.4.1Translocation Tissues - Phloem

8.4.2Translocation

8.4.3End of Topic Test - Plant Transport

9Transport in Animals

10Diseases & Immunity

10.1Diseases & Immunity

10.1.1Health Issues

10.1.2Causing Diseases

10.1.3Preventing Infection

10.1.4Human Defence Systems - Non-Specific Defences

10.1.5Human Defence Systems - Immune Systems

10.1.6Antibodies

10.1.7Vaccination & Immunity

10.1.8Passive Immunity

10.1.9Viruses

10.1.10End of Topic Test - Health & Disease

11Gas Exchange in Humans

11.1Gas Exchange in Humans

11.1.1Exchange Surface

11.1.2Lung Gas Exchange

11.1.3Alveoli

11.1.4Breathing Process

11.1.5Breathing Composition

11.1.6Breathing & Exercise

11.1.7Thorax

12Respiration

12.1Respiration

12.1.1Respiration Uses

12.1.2Investigating Respiration

12.1.3End of Topic Test - Respiration

12.1.4Exam-Style Questions - Respiration During Exercise

12.2Aerobic & Anaerobic Respiration

12.2.1Respiration Reactions

12.2.2Oxygen Use & Debt

12.2.3Aerobic and Anaerobic Respiration

13Excretion in Humans

13.1Excretion in Humans

13.1.1Excretion in Humans

13.1.2Urea

13.1.3Water Balance

13.1.4Water in Urine

13.1.5The Kidneys

13.1.6Urine Production

13.1.7Urinary System

13.1.8Dialysis

13.1.9Dialysis - Pros & Cons

13.1.10Kidney Transplants

13.1.11Kidney Transplants - Pros & Cons

14Coordination & Response

14.1Coordination & Response

14.1.1The Nervous System

14.1.2Reflex Actions

14.1.3Reflex Arc

14.1.4Synapses

14.1.5End of Topic Test - Nervous Control

14.1.6Exam-Style Questions - Nervous System

14.2Sense Organs

14.2.1Sense Organs

14.2.2Eye Anatomy

14.2.3Eye Function - Light

14.2.4Eye Function - Focus

14.2.5Eye Function - Detecting Colour

14.3Hormones

14.3.1Hormones in Humans

14.3.2Endocrine Glands

14.3.3Nervous vs Endocrine

14.3.4Adrenaline

14.4Homeostasis

14.4.1Homeostasis

14.4.2Regulating Internal Conditions

14.4.3Control Systems

14.4.4Negative Feedback

14.4.5Thermoregulation

14.4.6Thermoregulation - Hot and Cold

14.4.7Thermoregulation - Skin

14.4.8Thermoregulation - Sweating & Shivering

14.4.9Thermoregulation - Hairs

14.4.10Thermoregulation - Blood Vessels

14.4.11Blood Glucose

14.4.12Detecting Glucose

14.4.13Type 1 Diabetes

14.4.14End of Topic Test - Homeostasis & Hormones

14.4.15Grade 9 - Hormonal Coordination

14.5Tropic Responses

14.5.1Types of Tropisms

14.5.2Auxins and Tropisms

14.5.3Required Practical - Plant Hormones

15Drugs

15.1Drugs

15.1.1Antibiotics

15.1.2Antibiotic Resistance

15.1.3Resistant Bacteria

16Reproduction

16.1Asexual Reproduction

16.1.1Asexual Reproduction

16.1.2Advantages of Asexual Reproduction

16.2Sexual Reproduction

16.2.1Sexual Reproduction

16.2.2Gametes vs. Zygotes

16.2.3Advantages of Sexual Reproduction

16.3Sexual Reproduction in Plants

16.3.1Flower Anatomy

16.3.2Pollination Methods

16.3.3Self-pollination & Cross-polination

16.3.4Germination

16.4Sexual Reproduction in Humans

16.4.1Human Reproductive Systems - Male

16.4.2Human Reproductive Systems - Female

16.4.3Human Gametes - Sperm Cells

16.4.4Human Gametes - Egg Cells

16.4.5Human Gametes - Egg vs. Sperm

16.4.6Pregnancy

16.4.7Pregnancy Health

16.4.8Birth - Labour

16.4.9Birth - Breast-feeding

16.5Sex Hormones in Humans

16.5.1Puberty

16.5.2Menstruation

16.5.3Menstrual Cycle

16.5.4Menstrual Hormones

16.5.5Baby Planning

16.5.6Infertility

16.5.7Fertility Treatments Pros & Cons

16.5.8End of Topic Test - Reproductive Hormones

16.5.9Exam-Style Questions - Hormones & Contraception

16.6Sexually Transmitted Infections

16.6.1HIV

17Inheritance

18Variation & Selection

18.1Variation

18.1.1Variation

18.1.2Continuous & Discontinuous Variation

18.1.3Mutations

18.1.4Sickle Cell Symptoms

18.1.5Sickle Cell & Malaria

18.1.6Sickle Cell Inheritance

18.2Adaptive Features

18.2.1Adaptive Features

18.2.2Plant Adaptations

18.3Selection

18.3.1Natural Selection

18.3.2Evolution

18.3.3Antibiotic Resistance

18.3.4Selective Breeding

18.3.5Selective Breeding Process

18.3.6Uses of Selective Breeding

18.3.7Grade 9 - Evolution

18.3.8End of Topic Test - Variation & Evolution

19Organisms & Their Environment

20Human Influence on Ecosystems

21Biotechnology & Genetic Modification

21.1Biotechnology & Genetic Modification

21.1.1Bacteria in Biotechnology

21.2Biotechnology

21.2.1Yeast in Biotechnology

21.2.2Enzymes in Biotechnology

21.2.3Penicillin

21.3Genetic Modification

21.3.1Genetic Modification

21.3.2Genetic Modification - Process

21.3.3Genetic Modification - Controversy

21.3.4Pros & Cons of Genetic Modification

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