Topic B

How Plants Stay Alive

Start with light, water, and air, then connect photosynthesis, water movement, respiration, and plant responses to everyday observations.

A plant leaning toward a windowLeaves receiving lightWater changing in a pot

A plant physiology concept image with leaves, sunlight, water droplets, and moving air

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Light, sugar production and respiration

How water moves through a plant

Showing 37 of 37 articles

Light and energy

What is photosynthesis?

Photosynthesis is the process in which plants use light energy to turn water and carbon dioxide into sugars and other organic materials, releasing oxygen along the way.

Light and energy

Why do plants need sunlight?

Plants need usable light—not sunlight as food—to power photosynthesis and support growth. Light also helps plants respond to direction, day length, and seasons.

Light and energy

What is chlorophyll?

Chlorophyll is a light-absorbing pigment, not plant food. Learn how it works in chloroplasts, why many leaves look green, and what yellowing or variegation can suggest.

Water and transport

What is transpiration in plants?

Transpiration releases plant water as vapor, mainly through stomata. Follow the root-to-leaf route and distinguish transpiration, surface evaporation, and guttation.

Water and transport

How Does Water Move from Roots to Leaves?

Trace water from roots through xylem to leaves. Learn how transpiration tension drives long-distance flow and why that flow differs from osmosis across membranes.

Respiration and gas exchange

Do plants breathe?

Living plant cells respire day and night. Compare respiration with photosynthesis, distinguish gas exchange from cell chemistry, and learn why roots need oxygen.

Respiration and gas exchange

Why do roots need air?

Roots need oxygen for cellular respiration. Learn how water and air share pore spaces in potting mix, and why long-lasting saturation can slow root function.

Growth and environmental responses

Why do plants bend toward light?

Plants bend toward light because new growth responds to directional light. Learn how phototropism, auxin, shaded-side elongation, and window growing fit together.

Growth and environmental responses

Phototropism is a type of tropism: a directional plant growth response to light. Learn positive phototropism, negative phototropism, why plants have it, and how it differs from photosynthesis and leggy growth.

Flowering and dormancy

How do plants sense day and night?

Plants sense light without eyes. Learn how photoreceptors, circadian rhythms, and photoperiodism help plants track day, night, seasons, and the possible effects of light at night.

Flowering and dormancy

What Is Photoperiod in Plants?

Photoperiod describes daily light and dark duration. Compare short-day, long-day, and day-neutral flowering responses, and why a 12-hour cutoff is not universal.

Flowering and dormancy

Why Do Plants Flower?

Plants flower when they shift from leaf, stem, and root growth toward reproduction. Learn how maturity, day length, cool periods, and plant type affect flowering.

Flowering and dormancy

What Is Flower Bud Differentiation?

In gardening, flower bud differentiation often refers to the continuous development from flower-bud initiation through the formation of flowers and floral parts inside a bud. Learn how it relates to a visible bud and how maturity, seasonal cues, and plant type shape flowering development.

Growth and environmental responses

What Are Plant Hormones? How Plant Signals Shape Growth

Plant hormones are chemical signals made in very small amounts that help regulate growth, development, and responses to the environment. Learn how auxin, cytokinin, gibberellin, ABA, and ethylene work together.

Growth and environmental responses

What Is Auxin? How Plants Use Location and Concentration to Regulate Growth

Auxin is a class of plant hormones that helps shape growth according to where it is, how much is present, and which tissue receives it. Learn how it relates to phototropism, gravitropism, apical dominance, root formation, and cutting propagation.

Flowering and dormancy

Why Do Plants Go Dormant?

Plant dormancy is a pause in visible growth, not death. Learn why buds, seeds, bulbs, and crowns may pause growth—and how dormancy differs from slow winter growth and vernalization.

Flowering and dormancy

What Is Vernalization?

Vernalization is how sustained cold helps some plants gain the ability to flower or flower sooner. Learn how it differs from photoperiod, cold acclimation, dormancy, and cold stratification.

Mineral nutrients

If plants make their own sugars, why do they still need mineral nutrients?

Plants make sugars through photosynthesis but still need mineral nutrients. Learn how dissolved ions move from roots through xylem, and why N-P-K is only part of plant nutrition.

Mineral nutrients

What Are N, P, and K? Why Plants Need These Nutrients

What do N, P, and K do for plants? Learn their roles, the ions roots take up, how nutrients move through the plant, and why one symptom is not a diagnosis.

Growth and environmental responses

How Do Plants Grow Taller? From the Shoot Tip to Cell Elongation

How plants grow taller: new cells near the shoot tip, cell elongation, and lengthening young internodes—plus an animation showing which part of the stem grows.

Growth and environmental responses

How Do Plants Repair Wounds?

Plants often respond to injury by sealing wounds, compartmentalizing damaged tissue, and activating defense signals. Some tissues can regenerate, but closure is not full restoration.

Water and transport

What Does Water Do in Plants?

Water helps plants stay firm, move minerals, make sugars through photosynthesis, and cool leaves through transpiration. Learn why plant water is more than just moisture.

Water and transport

How do plants transport nutrients?

Learn how plants move water and mineral nutrients through xylem, distribute sugars through phloem, and shift source and sink roles as leaves and storage organs develop.

Growth and environmental responses

How Do Plants Sense Gravity? Why Roots Grow Down, Stems Grow Up, and What Gravitropism Means

Roots often grow downward and shoots often grow upward because growing plant tissues respond to gravity. Learn gravitropism, statoliths, auxin patterns, and why roots and shoots bend in different directions.

Light and energy

How Are C3, C4, and CAM Plants Different?

C3, C4, and CAM plants share photosynthesis but handle CO₂ differently. Compare spatial and temporal separation, stomata, photorespiration, heat, and water-use efficiency.

Growth and environmental responses

Why Do Some Plants Grow More Slowly Under Stress?

Drought, low light, unsuitable temperatures, salinity, and low root-zone oxygen can slow cell expansion and new growth. Learn how water, stomata, photosynthesis, and stress signals interact without treating slow growth as a diagnosis.

Mineral nutrients

What Are the Six Mineral Macronutrients Plants Need?

Learn what the six mineral macronutrients do in plants, why calcium, magnesium, and sulfur matter alongside NPK, and what 'macronutrient' actually means.

Water and transport

When Do Plants Close Their Stomata?

When do plants close their stomata? Learn how light, drought, heat, dry air, high VPD, leaf CO₂, and CAM photosynthesis shape stomatal opening and water loss.

Water and transport

What Happens to Plants When They Lack Water?

When plants face water stress, stomatal conductance and growth may decline before visible wilting. Learn how guard cells, ABA, turgor, transpiration, and prolonged water deficit fit together.

Mineral nutrients

What Are Root Nodules? What Do the Small Bumps on Legume Roots Do?

Root nodules are structures formed through cooperation between legume roots and rhizobia. Learn how symbiotic nitrogen fixation works and what root nodules can—and cannot—tell you.

Growth and environmental responses

How Do Plants Sense Touch? Mimosa, Tendrils, and Plant Movement

Plants can detect mechanical stimuli without an animal-like nervous system. Learn how mechanotransduction links force with Mimosa leaf closure, tendril coiling, and slower changes in plant form.

Flowering and dormancy

What Is a Plant Circadian Rhythm? How Light and Darkness Set the Clock

Plants have internal circadian rhythms that run on a roughly 24-hour cycle. Learn how light and darkness entrain the clock and shape leaf movement, stomata, growth, and seasonal responses.

Water and transport

How Do Plants Move Sugar?

Mature leaves often act as sugar sources, while growing roots, shoots, and fruits act as sinks. Learn how phloem moves sugars, how pressure flow works, and why these roles change.

Growth and environmental responses

What Is Ethylene? How Plants Use a Gaseous Hormone in Ripening, Leaf Fall, and Stress Responses

Ethylene is a gaseous plant hormone involved in fruit ripening, leaf senescence and abscission, and responses to wounding or flooding. Learn how diffusion, receptors, ACC, and hormone crosstalk shape its effects.

Light and energy

What Is Photorespiration? How Plants Recover Some Carbon

Photorespiration begins when Rubisco reacts with O₂ and produces 2-PG. It usually lowers net carbon assimilation in C3 plants, but its salvage pathway is still necessary.

Water and transport

What Are Diffusion and Osmosis? How Water and Gases Move in Plants

Diffusion moves particles down a concentration gradient, while osmosis is water moving across a selectively permeable membrane. Use stomata, root cells, and xylem to see how water and gases move through plants.

Light and energy

Light Reactions and the Electron Transport Chain: How Plants Make ATP and NADPH

Follow light energy, electrons, H⁺, and carbon through the chloroplast to see how light-dependent reactions make ATP and NADPH without directly making sugar.

How Plants Stay Alive

Find an article in this topic

Follow a connected reading path

Light, sugar production and respiration

How water moves through a plant

What is photosynthesis?

Why do plants need sunlight?

What is chlorophyll?

What is transpiration in plants?

How Does Water Move from Roots to Leaves?

Do plants breathe?

Why do roots need air?

Why do plants bend toward light?

What Is Phototropism?

How do plants sense day and night?

What Is Photoperiod in Plants?

Why Do Plants Flower?

What Is Flower Bud Differentiation?

What Are Plant Hormones? How Plant Signals Shape Growth

What Is Auxin? How Plants Use Location and Concentration to Regulate Growth

Why Do Plants Go Dormant?

What Is Vernalization?

If plants make their own sugars, why do they still need mineral nutrients?

What Are N, P, and K? Why Plants Need These Nutrients

How Do Plants Grow Taller? From the Shoot Tip to Cell Elongation

How Do Plants Repair Wounds?

What Does Water Do in Plants?

How do plants transport nutrients?

How Do Plants Sense Gravity? Why Roots Grow Down, Stems Grow Up, and What Gravitropism Means

How Are C3, C4, and CAM Plants Different?

Why Do Some Plants Grow More Slowly Under Stress?

What Are the Six Mineral Macronutrients Plants Need?

When Do Plants Close Their Stomata?

What Happens to Plants When They Lack Water?

What Are Root Nodules? What Do the Small Bumps on Legume Roots Do?

How Do Plants Sense Touch? Mimosa, Tendrils, and Plant Movement

What Is a Plant Circadian Rhythm? How Light and Darkness Set the Clock

How Do Plants Move Sugar?

What Is Ethylene? How Plants Use a Gaseous Hormone in Ripening, Leaf Fall, and Stress Responses

What Is Photorespiration? How Plants Recover Some Carbon

What Are Diffusion and Osmosis? How Water and Gases Move in Plants

Light Reactions and the Electron Transport Chain: How Plants Make ATP and NADPH

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