Plant Biology Notes

Gymnosperms and Angiosperms

• Gymnosperms: Naked seed plants; seeds not encased in fruit, do not produce flowers.

• Angiosperms: Seeds encased in fruit, produce flowers.

• Cambium Layer: Both groups have this; a layer of meristematic tissue able to continuously produce new (secondary) tissue, enabling continuous growth.

• Examples:

  • Gymnosperms: Cone-producing trees like pines.

  • Angiosperms: Plants that produce flowers with reproductive structures containing eggs (ovules).

Plant Nutrition

• Photosynthesis: Plants use atmospheric $CO_2$ and water to make carbohydrates.

• Nutrients: Needed from the soil to produce proteins, lipids, and other organic compounds.

• Macronutrients: Nutrients needed in large quantities:

  • Calcium

  • Phosphorus

  • Magnesium

  • Sulfur

  • Potassium

  • Nitrogen (especially important)

• Micronutrients: Nutrients needed in small quantities (e.g., iron, boron, chlorine, sodium).

Nitrogen as a Limiting Factor

• Atmospheric Nitrogen: 78% of Earth's atmosphere is nitrogen ($N_2$), but plants can't use it in this form.

• Limiting Factor: A chemical whose unlimited quantity leads to unlimited growth.

• Usable Forms of Nitrogen: Ammonium or nitrates.

• Source of Nitrogen: Plants get nitrogen from the soil.

• Unlimited Growth: Can cause pollution.

Red Tides and Algal Blooms

• Red Tides: Observed since the 1500s in Florida, now 10-15 times more common.

• Cause: Agricultural and sewage runoff into the Gulf of Mexico.

• Problem Species: Karenia brevis.

• Density: Can exceed tens of millions of cells per liter of seawater during a red tide.

• Agricultural Runoff: Rain carries nitrates from fertilizers into the Gulf, promoting Karenia brevis growth.

Red Tide Toxins

• Brevitoxin: A neurotoxin produced by Karenia brevis.

• Mechanism: Binds to gated sodium channels, stopping neurons from firing.

• Effect: Primarily affects neurons in the respiratory tract due to aerosolized toxins.

• Exposure Routes:

  • Inhalation: Breathing in aerosolized brevitoxins.

  • Ingestion: Swallowing seawater.

• Increased Toxin Production: Nitrogen presence increases toxin production per cell.

Harmful Algal Blooms

• Algal Bloom: Unlimited growth of a particular algae species.

• Color: Karenia brevis blooms appear more pukey green than red.

• Mobility: These phytoplankton have flagella that allows them to actively swim to the surface to photosynthesize.

• Exposure Risks: Ingestion, inhalation, topical.

Human Health Effects

• Symptoms: Vary from person to person, especially affecting those with underlying lung disease.

• Treatment:

  • Moving away from the exposed area.

  • Symptomatic support.

  • Inhaled medications for asthma exacerbation.

• Histamine Release: Toxin causes histamine release leading to sinus headaches and constricted airways.

• Skin Rashes: Possible in the water, especially for those with sensitive skin.

• Foam Toxicity: Foam can be 10 times more toxic than the water.

Neurotoxic Shellfish Poisoning

• Cause: Eating infected shellfish.

• Symptoms: Nausea, vomiting, diarrhea.

• Commercial Shellfish: Monitored for toxins.

• Homemade Shellfish: Risk of exposure if harvesting your own shellfish.

Pet Health

• Pet Deaths: Usually due to consuming dead fish.

• Toxin Accumulation: Accumulates in the guts of fish.

• Symptoms: Gastrointestinal upset, confusion.

• Precautions: Prevent pets from playing in foam and rinse them off after swimming.

Nitrogen Cycle and Plants

• Fixation: Bacteria convert atmospheric nitrogen gas to ammonia.

• Ammonia/Ammonium: Can be taken up by plants.

• Amino Acids: Nitrogen is crucial for the synthesis of amino acids.

• Proteins: Amino acids are used to make proteins.

• Symbiotic Relationship: Some plants have bacteria in nodules around their roots that produce ammonia.

• Nitrites: Some bacteria turn ammonia into nitrites ($NO_2^-$), which are toxic to plants.

• Nitrates: Other bacteria convert nitrites into nitrates, which are beneficial for plants.

Impact on Photosynthesizers

• Nitrates and Algae: All photosynthesizers, including algae, love nitrates.

• Harmless Algae: Excess fertilizer runoff can cause algal blooms in lakes (e.g., Lake Estelle), clouding the water.

Decomposition

• Decomposition: Dead organisms are broken down by decomposers (fungi and bacteria).

• Nutrient Conservation: Decomposers conserve nitrogen from dead organisms by taking up species that have nitrogen.

• Modification: Breaking down a nitrogenous substance to conserve biological nitrates.

Movement of Water and Minerals in Plants

• Xylem: Tissue that takes water and minerals from the ground up towards stem and leaf.

  • Cell Types: Tracheids and vessels.

    • Tracheids: Continuous tubes for water transport.

    • Vessels: Join end-to-end to make elongated tubes.

  • Pressure Gradient: From root hairs to distant parts of the plant, aiding upward movement of water.

  • Transpirational Pull: Evaporation at the leaves creates suction to pull water up.

  • Adhesion: Water sticks to other substances, preventing backward flow.

• Phloem: Moves food and organic compounds (e.g., sucrose) produced in the leaves down towards stem and roots.

  • Sucrose: Most abundant organic compound in the phloem.

  • Concentration Gradient: Sucrose concentration decreases from leaves to roots.

  • Cell Types: Sieve cells and companion cells.

    • Sieve Cells: Form the sieve tube; lose nuclei and other organelles.

    • Companion Cells: Carry out nuclear functions, producing proteins for the sieve cells.

Tropisms

• Tropism: A growth response to environmental stimulus (positive or negative).

  • Phototropism: Positive; growing towards the light.

  • Hydrotropism: Positive; growing towards water.

  • Geotropism: Negative; growing away from gravity.

Photoperiodism

• Photoperiod: The amount of daylight during a certain time of year.

• Detection: Humans and plants can detect photoperiod.

• Humans: Pineal gland produces melatonin and serotonin.

  • SAD (Seasonal Affective Disorder): Sadness in winter due to less daylight.

  • Treatment: Light therapy simulating sunlight.

• Plants: Use phytochrome.

  • Phytochrome Forms: $P<em>r$ (red light) and $P</em>{fr}$ (far-red light).

  • Mechanism: Different concentrations of $P<em>r$ and $P</em>{fr}$ help plants detect the amount of daylight in a certain time period.

  • Seasonal Growth: Plants regulate seasonal growth based on photoperiod detection.