Lesson 10 + 11 Tropisms + Biomes and Climate Change

Biome

A major geographical region with similar environmental conditions and types of life.

Ecosystem

A community of living organisms interacting with each other and their non-living environment.

Habitat

The place where an organism lives.

Factors Defining Biomes

Climate, especially temperature and precipitation, and the vegetation found in a region.

Biomes as Open Systems

Biomes exchange both matter and energy with their surroundings.

Open System

A system that exchanges matter and energy with its surroundings, such as a biome or human cell.

Closed System

A system that exchanges energy but not matter with its surroundings; Earth is an approximate example.

Tundra

A cold biome with low-growing vegetation, little precipitation, and few trees.

Taiga

A biome with long, cold winters dominated by coniferous trees; also called boreal forest.

Deciduous Forest

A forest biome with trees that shed their leaves seasonally.

Grassland

A biome dominated by grasses, with relatively few trees; includes prairies and savannas.

Rainforest

A biome with abundant precipitation and dense vegetation.

Desert

A biome with very low precipitation and sparse vegetation.

Weather

Short-term atmospheric conditions that can change from hour to hour or day to day.

Climate

Long-term weather patterns of a region, usually measured over at least 30 years.

Two Major Factors Determining Biomes

Temperature and precipitation, which affect water availability and species survival.

Latitude and Temperature

Solar radiation varies with latitude; places closer to the equator generally receive more direct sunlight.

Altitude and Temperature

According to the notes, temperature drops about 4.5°C for each 1,000 m increase in altitude.

Climatograph

A graph showing a region’s temperature and precipitation together.

Biosphere as a Dynamic System

The biosphere changes over Earth’s history rather than remaining constant.

Paleoclimate

The study of past climate conditions.

Evidence of Past Climate

Glacier ice cores, lake sediments, plant fossils, tree cores, and preserved pollen.

Ice Cores

Ancient glacier ice containing trapped gases that help scientists study past atmospheric conditions.

Changes in Earth’s Tilt

A natural cause of climate change; the tilt varies from about 22.3° to 24.5°.

Greater Axial Tilt

A greater tilt makes the polar regions warmer in their summer, increasing seasonal contrasts.

Tectonic Activity and Climate

Continental movements change geographic positions and can alter local climates.

Human-Caused Climate Change

Recent rapid global warming is attributed largely to human activities.

IPCC

Intergovernmental Panel on Climate Change: established in 1988 to assess climate research and risks.

Ocean Conveyor Belt

Large-scale ocean circulation that moves water and heat around Earth.

Plant Stimulus

A change in the environment, such as light, gravity, touch, or darkness, that triggers a response.

Tropism

A directional plant growth response to an environmental stimulus.

Phototropism

Plant growth in response to light; stems commonly grow toward a light source.

Benefit of Phototropism

Growing toward light maximizes light exposure and supports photosynthesis.

Auxin

A plant hormone that regulates growth and helps control phototropism and gravitropism.

Phototropism Mechanism

The shoot tip senses light; auxin builds up on the shaded side, increasing cell elongation and bending the stem toward light.

Darwin’s Phototropism Experiment

Showed that the seedling tip detects light and sends a growth-controlling signal to the stem.

Boysen-Jensen’s Experiment

Gelatin allowed the growth signal to pass, while mica blocked it, supporting a chemical signal.

Went’s Auxin Experiment

Auxin diffused into agar; an off-centre auxin-containing block caused a seedling to curve.

Gravitropism

A plant growth response to Earth’s gravitational force.

Positive Gravitropism

Growth toward gravity, as seen when roots grow downward.

Negative Gravitropism

Growth against gravity, as seen when stems grow upward.

Amyloplasts and Statoliths

Starch-containing structures involved in gravity detection and auxin redistribution.

Auxin in Stems During Gravitropism

Auxin stimulates elongation on the lower side, causing the stem to curve upward.

Auxin in Roots During Gravitropism

Auxin inhibits elongation on the lower side, causing the root to curve downward.

Nastic Response

A non-directional plant movement in response to an external stimulus.

Turgor Pressure

Water pressure inside plant cells; rapid changes can cause some nastic movements.

Touch-Induced Nastic Responses

The Venus flytrap closes its trap and the Mimosa plant folds its leaves in response to touch.

Sleep Movements

Closing petals or drooping leaves in response to darkness, often through changes in turgor pressure.

Tropism vs. Nastic Response

Tropisms are directional growth responses; nastic responses do not depend on stimulus direction.