91Ó°ÊÓ

A student randomly chose 40 tobacco seeds of the same species from a packet. He placed 20 seeds on moist paper towels in each of two petri dishes. He wrapped dish A completely in an opaque cover to exclude all light. He did not wrap dish B. He placed the dishes equidistant from a light source set to a cycle of 14 hours of light and 10 hours of dark. All other conditions were the same for the two dishes. He examined the dishes after 7 days, and permanently removed the opaque cover from dish A. This table shows the student’s data. The most probable cause for the difference in mean stem length between plants in dish A and plants in dish B is ____. a. shortening of cells in the stem in response to the lack of light b. elongation of the stem in response to the lack of light c. enhancement of stem elongation by light d. genetic differences between the seeds

Step by step solution

01

Understand the experiment

The student placed 20 tobacco seeds in each of two petri dishes. Dish A was wrapped to exclude light, while dish B was not. Both dishes were placed equidistant from a light source with a 14-hour light and 10-hour dark cycle. This set up an experiment to compare the growth of the seeds under different light conditions.

02

Identify the Conditions

Dish A had seeds grown in complete darkness for 7 days, whereas Dish B had seeds that were exposed to regular cycles of light and dark. The only variable that was different between the two dishes was the presence or absence of light.

03

Analyze the Data

The student observed the plants after 7 days and recorded the mean stem length. The mean stem length for the plants in each dish should be looked at carefully to understand the effect of the presence or absence of light.

04

Consider plant physiology

In general, plants grown in darkness tend to have elongated stems as they 'stretch' towards the light in a process called etiolation. This is a known response where plants elongate their stems in an attempt to reach a light source.

05

Choose the correct answer

Based on plant physiology, the most likely cause for the difference in mean stem length between plants in dish A (darkness) and dish B (light) is the elongation of the stem in response to the lack of light (etiolation). This matches option b.

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

plant physiology

Plants, just like animals, have specific systems and processes that help them grow and survive. This is known as plant physiology. It includes processes like photosynthesis, respiration, and nutrient uptake. All these processes are influenced by external factors such as light, water, and temperature. When seeds germinate, they rely on stored energy. As they grow, plants need light for photosynthesis, a process that converts light into energy. This conversion happens in the chloroplasts, which contain chlorophyll. In the absence of light, plants exhibit certain physiological changes. They may elongate their stems excessively, a condition known as etiolation. This is an adaptive response to help the plant reach for light.

light exposure effects

Light is a crucial factor for plant growth. It affects various aspects of plant development, from seed germination to flowering and fruiting. The quality, intensity, and duration of light influence how plants grow. When exposed to light, plants perform photosynthesis, creating the energy they need to thrive. This process uses light, carbon dioxide, and water to produce glucose and oxygen. If plants do not receive enough light, they undergo etiolation. Etiolated plants have pale yellow leaves and long stems. This is because they are trying to grow taller to reach a light source. Without light, chlorophyll does not develop properly, leading to pale or yellow leaves.

seed germination

Seed germination is the process by which a seed develops into a new plant. This begins with water uptake, causing the seed to swell and break its coat. The embryo inside the seed starts to grow. Germination is influenced by environmental factors like water, temperature, and light. For some seeds, light is a trigger for germination. Once the seed sprouts, the seedling needs light to start photosynthesis. In an experiment where one set of seeds is grown in darkness and another in light, the ones in darkness will show elongation as they seek light. This is a survival mechanism known as etiolation. Whereas seeds grown in light will develop normally, with green chlorophyll and sturdy stems.