Stomata Lab+Exercise Lab

Which substances move into and out of the plant through the stomata?

Water moves out of the plant through the xylem and sugar moves in the plant through the phloem.

 What signals stomate guard cells to open/close?

A signal to open is when the plant is lacking food and needs sugar. A signal to close is when the CO2 levels are too high

Why is the opening vs. closing of stomata on a hot summer day a compromise?

On a hot summer day, stomata must balance allowing CO₂ in for photosynthesis with minimizing water loss through transpiration, making their opening and closing a compromise between energy production and water conservation.

How have the number of stomata on plants been used to study CO₂ and temperature levels in Earth's past?

Plants are in tune with their environments so there are many signals that can be obtained from fossil plants like what temperature they lived in, the atmospheric environment, and the carbon dioxide concentration. The levels of carbon dioxide have changed on Earth and if a plant had less stomata during a high carbon time they had an advantage. During low-carbon times, plants had to have many stomata to scrape up enough CO2 not to die.

How does stomatal density relate to a plant's environment?

Stomatal density is influenced by environmental factors like humidity, CO₂ levels, and water availability. Plants in dry environments (e.g., cacti, succulents) have fewer stomata to minimize water loss, while plants in humid environments (e.g., ferns, tropical plants) have more stomata to maximize gas exchange.

Why would a plant have fewer stomata on its upper epidermis compared to its lower epidermis?

The upper epidermis is more exposed to sunlight and heat, which increases transpiration. By having fewer stomata on the upper epidermis, the plant reduces excessive water loss while still allowing gas exchange through the lower epidermis, which is more shaded and cooler.

What is the relationship between stomatal openness and transpiration rate?

Greater stomatal openness leads to a higher transpiration rate, as more water vapor escapes from the leaf. This helps cool the plant but also increases water loss. Conversely, reduced stomatal openness decreases transpiration, conserving water but limiting CO₂ intake for photosynthesis.

How does temperature affect stomatal behavior?

In high temperatures, stomata may close to prevent excessive water loss. In cooler temperatures, stomata may open more to facilitate gas exchange since the risk of dehydration is lower.

What adaptations would you expect to see in a desert plant’s stomata?

• Fewer and smaller stomata to reduce water loss.

• Sunken stomata or stomata located in pits to trap moisture.

• Stomatal closure during the day and opening at night (CAM photosynthesis) to minimize water loss while still allowing CO₂ uptake.

Why might a floating aquatic plant have stomata only on its upper epidermis?

Since the underside is submerged, it cannot exchange gases with the air. Having stomata only on the upper surface allows the plant to absorb CO₂ for photosynthesis and release O₂ effectively.

What is the significance of stomatal distribution in grass species like oats?

Grass species, including oats, have stomata on both sides of their leaves because their vertical orientation limits direct sun exposure to a single surface. This allows efficient gas exchange regardless of how the leaves are positioned.

What evidence from fossilized leaves can scientists use to infer past CO₂ levels?

Scientists examine stomatal density in fossilized leaves. Lower stomatal density indicates higher past CO₂ levels, while higher stomatal density suggests lower CO₂ levels, as plants needed more stomata to absorb sufficient CO₂ for photosynthesis.

Your heart rate has to increase during exercise to bring more oxygen to your muscle cells. Why do your muscle cells need more oxygen?

This makes sense because when you exercise your muscle cells need more ATP energy from cellular respiration so your heart has to beat faster to pump more oxygen-rich Red Blood cells from your lungs to your muscle cells.

Describe two mechanisms by which your heart "knows" to increase its rate of contraction during exercise.

• Nervous System Regulation (Sympathetic Nervous System Activation):

  • During exercise, the sympathetic nervous system is activated, sending signals from the brain's medulla oblongata to the heart. This leads to the release of norepinephrine, which binds to receptors on the sinoatrial (SA) node, causing the heart to beat faster and contract more forcefully.

• Chemoreceptor and Hormonal Response:

  • Chemoreceptors in the aortic arch and carotid arteries detect increased levels of CO₂ and decreased O₂ in the blood. They send signals to the brain to increase heart rate, ensuring more oxygen is delivered to muscles.

  • The adrenal glands release epinephrine (adrenaline), which further stimulates the heart to beat faster and enhances blood flow to active muscles.

What is metabolism, and how do catabolism and anabolism differ?

• Metabolism refers to all chemical reactions in the body that sustain life, including energy production and molecule synthesis.

• Catabolism involves breaking down molecules (e.g., glucose, fats) to release energy.

• Anabolism involves building complex molecules (e.g., proteins, DNA) using energy.

Why are carbohydrates and fats used as primary energy sources, while proteins are conserved?

• Carbohydrates and fats are more efficient energy sources because they provide a high ATP yield without producing toxic byproducts.

• Proteins are primarily used for growth, repair, and enzyme function; breaking them down for energy leads to ammonia production, which is toxic.

How does thyroid hormone influence cellular respiration and metabolic rate?

Thyroid hormones (T3 and T4) increase the rate of cellular respiration by stimulating mitochondrial activity, enhancing ATP production, and raising overall metabolic rate.

Write the balanced chemical equation for cellular respiration.

C6​H12​O6​+6O2​→6CO2​+6H2​O+ATP

What are the two main functions of breathing?

• Oxygen intake for cellular respiration.

• Carbon dioxide removal to maintain pH balance and prevent acidosis.

How does oxygen move from the lungs into muscle cells?

Oxygen diffuses from alveoli into the blood, binds to hemoglobin, is transported via circulation, and diffuses into muscle cells due to the partial pressure gradient.

What happens to carbon dioxide after it is produced in muscle cells?

CO₂ diffuses into the blood, where it is transported in three ways:

• Dissolved in plasma (7-10%)

• Bound to hemoglobin (20-30%)

• As bicarbonate ions (60-70%) via the carbonic acid-bicarbonate buffer system.

How does the autonomic nervous system regulate heart and lung function during exercise?

• The sympathetic nervous system increases heart rate, stroke volume, and bronchodilation.

• The parasympathetic nervous system slows heart rate and constricts airways post-exercise.

What role do chemoreceptors play in maintaining homeostasis of blood gases?

• Peripheral chemoreceptors (carotid and aortic bodies) detect low O₂ and high CO₂ levels, triggering increased breathing and heart rate.

• Central chemoreceptors (medulla oblongata) detect pH changes from CO₂ buildup, adjusting respiration accordingly.

How do the adrenal glands contribute to the body's response to exercise?

They release epinephrine and norepinephrine, increasing heart rate, blood pressure, and glucose availability for energy.

Why does heart rate increase during exercise?

To pump more oxygenated blood to active muscles and remove CO₂ faster.

How does stroke volume contribute to increased cardiac output during exercise?

Stroke volume (blood pumped per beat) increases due to stronger heart contractions, leading to higher cardiac output (CO = HR × SV).

Describe the role of hemoglobin in oxygen transport.

Hemoglobin in red blood cells binds O₂ in the lungs and releases it to tissues based on oxygen demand.

What physiological changes occur to increase oxygen delivery during exercise?

Increased heart rate, stroke volume, breathing rate, and capillary dilation. Bohr effect (lower pH enhances oxygen unloading).

How does the redistribution of blood flow during exercise help muscle cells?

Blood is redirected from non-essential organs (digestive system, kidneys) to active muscles for more oxygen and nutrient delivery.

Why does anaerobic metabolism occur at the beginning of exercise?

Oxygen delivery lags behind demand, so muscles temporarily use anaerobic glycolysis, producing ATP rapidly but also lactic acid.

What are the short-term effects of exercise on respiration and circulation?

Increased heart rate, stroke volume, blood pressure, and breathing rate. Vasodilation in muscles and vasoconstriction in non-essential organs.

How does long-term aerobic exercise improve cardiovascular efficiency?

Strengthens heart muscle, increases stroke volume, lowers resting heart rate, and enhances capillary networks in muscles.

Why do trained athletes have a lower resting heart rate than non-athletes?

Their heart muscle is stronger, allowing a higher stroke volume, so fewer beats are needed to maintain circulation.

How does regular aerobic exercise impact the risk of developing chronic diseases?

Reduces the risk of heart disease, hypertension, diabetes, obesity, and improves lung function and cholesterol levels.