Problem 3 - Biology Today and Tomorrow with Physiology

Question

Bryophytes have independent ____ and attached, dependent ____. a. sporophytes; gametophytes b. gametophytes; sporophytes

Step-by-Step Solution

Answer

b. gametophytes; sporophytes

Step 1: Understanding Bryophyte Life Cycle

Bryophytes, which include mosses, liverworts, and hornworts, have a distinct life cycle known as alternation of generations. This involves both a gametophyte stage and a sporophyte stage. Understanding which stage is independent or dependent is key to answering the question.

Step 2: Identify the Independent Structure

In bryophytes, the gametophyte is the dominant and independent part of the life cycle. It is the stage that carries out photosynthesis and is self-sufficient, able to live on its own.

Step 3: Pinpoint the Dependent Structure

The sporophyte in bryophytes is dependent on the gametophyte. Once the sporophyte develops from the fertilized gametes, it remains attached to and receives nutrients from the gametophyte, as it does not perform photosynthesis independently.

Step 4: Review the Answer Options

Given that the gametophyte is independent and the sporophyte is dependent, we should match this information with the provided options: a. sporophytes; gametophytes b. gametophytes; sporophytes The correct option should reflect gametophytes being independent and sporophytes being dependent.

Step 5: Select the Correct Answer

Option b correctly reflects the life cycle of bryophytes, where the gametophytes are independent and the sporophytes are attached and dependent on the gametophytes.

Key Concepts

Gametophyte

In the world of bryophytes, the gametophyte is a very important stage. It is the green, leafy part of the plant that you likely see growing on rocks or trees in a shady forest.
This stage in the life cycle of bryophytes is called the dominant stage because it is the longest-lived and most visible part of their life cycle. Gametophytes perform photosynthesis, which means they use sunlight to make food and energy.

• The gametophyte is independent, meaning it does not rely on another plant structure for survival.
• It produces gametes, which are reproductive cells like sperm and eggs.
• Through this stage, bryophytes can spread and adapt to various environments.

As it carries out photosynthesis, the gametophyte provides nutrients not only for itself but also for its dependent partner, the sporophyte.

Sporophyte

The sporophyte is the other main stage in the bryophyte life cycle, but unlike the gametophyte, it is not independent. It grows from the fertilized egg produced by the gametophyte, forming a structure that releases spores.
It is dependent on the gametophyte for nutrients because it is attached to it and cannot perform photosynthesis.

• Sporophytes grow out of the gametophyte's tissues and often resemble a stalk.
• Their primary role is to produce spores, which spread to form new gametophytes.
• The release and distribution of these spores are crucial for the continuation of the species.

Without the gametophyte, the sporophyte would not survive or fulfill its role, emphasizing how they rely on each other in the bryophyte life cycle.

Alternation of Generations

Alternation of generations is a fascinating reproductive cycle seen in bryophytes. This cycle alternates between two stages: the gametophyte and the sporophyte.
It is a continuous cycle that ensures the survival and propagation of the species across generations.

• The gametophyte generation produces gametes through a process called mitosis.
• Gametes from the gametophyte combine during fertilization to create the sporophyte.
• The sporophyte generation produces spores through meiosis.

These spores then grow to become new gametophytes, perpetuating the cycle. This process shows the dynamic ways bryophytes adapt and thrive in their environments.

Mosses

Mosses are perhaps the most familiar group of bryophytes and serve as a great example to illustrate this special life cycle.
Mosses are found virtually everywhere — from gardens and sidewalks to dense forests. They can thrive in places where other plants can't due to their resilience.

• Mosses have a high dependency on moist environments, as they need water to reproduce.
• The green, carpet-like structures we often notice are the gametophytes, taking part in photosynthesis.
• Attached stalks hold up tiny capsules, which are the sporophytes, releasing spores into the wind for propagation.

Mosses help to prevent soil erosion and act as a habitat for small organisms, showcasing their importance in different ecosystems.

Photosynthesis in Plants

Photosynthesis is a critical process in plants, allowing them to use sunlight to convert carbon dioxide and water into glucose and oxygen — their food and energy sources.
In bryophytes like mosses, it is primarily the gametophyte that performs this essential function.

• The presence of chlorophyll in gametophytes allows them to capture sunlight.
• Photosynthesis occurs in structures known as chloroplasts within the plant cells.
• This process not only provides energy for the plant but also for the non-photosynthetic parts like the sporophyte.

Through photosynthesis, bryophytes play a crucial role in carbon cycling and contribute to oxygen production, underlining their value to the environment and the biosphere at large.