Enlist the steps of controlled cross pollination. Would emasculation be needed in a cucurbit plant? Give reaso

NCERT Exemplar · Q21

Q. Enlist the steps of controlled cross pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.

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Concept understanding — Bagging Technique Utility

Let’s begin with something you already know from everyday life.

Imagine you have to make a very important decision — say, which college course to pick. You could ask one friend for advice. But that one friend might be biased (they love their own subject) or misinformed (they heard something wrong). So instead, you ask ten different people — teachers, seniors, parents, counsellors — and then take a majority vote or an average of their opinions. That collective decision is almost always more reliable than any single person’s advice.

That is the core intuition behind Bagging.

What Bagging Does

In data analysis and machine learning, Bagging stands for Bootstrap Aggregating. It is a technique used to make a prediction model more stable and accurate.

Here is the precise meaning: instead of building one single model (like one decision tree or one rule-based classifier) on the entire dataset, you create many slightly different versions of the same model, each trained on a different random sample of the original data. Then you combine all their outputs — usually by taking a majority vote (for classification) or an average (for prediction).

The key word is Bootstrap. A bootstrap sample is created by randomly picking data points from the original dataset with replacement — meaning the same data point can be picked more than once in a single sample, and some points may be left out. Each sample is different, so each model sees a slightly different view of the world.

Why It Matters

The main utility of Bagging is reducing variance — that is, reducing the model’s tendency to change wildly if you give it a slightly different set of data.

Think of it this way: a single model can be “nervous” — it might overreact to a few unusual data points (outliers) or to random noise in the data. But when you average the opinions of many such models, their individual nervousness cancels out. The combined model becomes calm, stable, and more accurate.

Important

Bagging works best when the individual models are unstable — meaning they change a lot with small changes in the training data. Decision trees are a classic example. Bagging turns a shaky tree into a robust forest.

Key Points to Remember (for exams)

Purpose: To improve accuracy and stability by combining multiple models.
How it works: Create many random samples (with replacement) from the original data. Train a separate model on each sample. Combine their predictions.
Why it helps: Reduces overfitting (the model memorising noise) and lowers variance.
Trade-off: It does not reduce bias much — if the individual model is fundamentally weak, bagging won’t fix that. It only makes a good model more reliable. …

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Controlled cross-pollination is a deliberate technique to transfer pollen from one plant to another, and emasculation is not needed in cucurbit plants because they have unisexual flowers.

Controlled cross-pollination is a fundamental technique in plant breeding, used to create hybrids with desired traits. The process ensures that only the intended pollen fertilises the chosen female parent, preventing unwanted self-pollination or contamination from other plants. This is especially important when you want to combine specific characteristics from two different parent plants, such as disease resistance from one and high yield from another.

The steps of controlled cross-pollination, as outlined in NCERT, are carefully sequenced to maintain genetic purity. First, you select the female parent plant — the one that will receive the pollen. Before the flower buds open (a stage called the bud stage), you must remove the anthers from these buds. This removal of anthers is called emasculation. Emasculation prevents self-pollination because the flower can no longer produce its own pollen. After emasculation, you cover the flower with a bag made of waterproof material, such as butter paper or muslin cloth. This bagging step protects the emasculated flower from any stray pollen carried by wind or insects.

Next, you select the male parent plant — the one that will provide the pollen. When the male parent’s flowers are mature and releasing pollen, you collect the pollen grains, often by gently tapping the flower over a clean container. You then transfer this pollen to the stigma of the emasculated female flower. This step is called pollination. Immediately after pollination, you re-bag the female flower to keep it protected until the fruit develops. The final step is to label the bag with details of the parents and the date, so the resulting seeds can be traced back to the specific cross.

Note

In some plants, like peas, the flowers are bisexual (contain both male and female parts), so emasculation is essential. But in plants with unisexual flowers, the situation is different. …

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Q.Enlist the steps of controlled cross pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.

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